Develop Reference

turn long html into text in a short and efficient way (js) [duplicate]

I have the following code in Ruby. I want to convert this code into JavaScript. What is the equivalent code in JS?
text = <<"HERE"
This
Is
A
Multiline
String
HERE

Update:
ECMAScript 6 (ES6) introduces a new type of literal, namely template literals. They have many features, variable interpolation among others, but most importantly for this question, they can be multiline.
A template literal is delimited by backticks:
var html = `
<div>
<span>Some HTML here</span>
</div>
`;
(Note: I'm not advocating to use HTML in strings)
Browser support is OK, but you can use transpilers to be more compatible.
Original ES5 answer:
Javascript doesn't have a here-document syntax. You can escape the literal newline, however, which comes close:
"foo \
bar"

ES6 Update:
As the first answer mentions, with ES6/Babel, you can now create multi-line strings simply by using backticks:
const htmlString = `Say hello to
multi-line
strings!`;
Interpolating variables is a popular new feature that comes with back-tick delimited strings:
const htmlString = `${user.name} liked your post about strings`;
This just transpiles down to concatenation:
user.name + ' liked your post about strings'
Original ES5 answer:
Google's JavaScript style guide recommends to use string concatenation instead of escaping newlines:
Do not do this:
var myString = 'A rather long string of English text, an error message \
actually that just keeps going and going -- an error \
message to make the Energizer bunny blush (right through \
those Schwarzenegger shades)! Where was I? Oh yes, \
you\'ve got an error and all the extraneous whitespace is \
just gravy. Have a nice day.';
The whitespace at the beginning of each line can't be safely stripped at compile time; whitespace after the slash will result in tricky errors; and while most script engines support this, it is not part of ECMAScript.
Use string concatenation instead:
var myString = 'A rather long string of English text, an error message ' +
'actually that just keeps going and going -- an error ' +
'message to make the Energizer bunny blush (right through ' +
'those Schwarzenegger shades)! Where was I? Oh yes, ' +
'you\'ve got an error and all the extraneous whitespace is ' +
'just gravy. Have a nice day.';

the pattern text = <<"HERE" This Is A Multiline String HERE is not available in js (I remember using it much in my good old Perl days).
To keep oversight with complex or long multiline strings I sometimes use an array pattern:
var myString =
['<div id="someId">',
'some content<br />',
'someRefTxt',
'</div>'
].join('\n');
or the pattern anonymous already showed (escape newline), which can be an ugly block in your code:
var myString =
'<div id="someId"> \
some content<br /> \
someRefTxt \
</div>';
Here's another weird but working 'trick'1:
var myString = (function () {/*
<div id="someId">
some content<br />
someRefTxt
</div>
*/}).toString().match(/[^]*\/\*([^]*)\*\/\}$/)[1];
external edit: jsfiddle
ES20xx supports spanning strings over multiple lines using template strings:
let str = `This is a text
with multiple lines.
Escapes are interpreted,
\n is a newline.`;
let str = String.raw`This is a text
with multiple lines.
Escapes are not interpreted,
\n is not a newline.`;
1 Note: this will be lost after minifying/obfuscating your code

You can have multiline strings in pure JavaScript.
This method is based on the serialization of functions, which is defined to be implementation-dependent. It does work in the most browsers (see below), but there's no guarantee that it will still work in the future, so do not rely on it.
Using the following function:
function hereDoc(f) {
return f.toString().
replace(/^[^\/]+\/\*!?/, '').
replace(/\*\/[^\/]+$/, '');
}
You can have here-documents like this:
var tennysonQuote = hereDoc(function() {/*!
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die
*/});
The method has successfully been tested in the following browsers (not mentioned = not tested):
IE 4 - 10
Opera 9.50 - 12 (not in 9-)
Safari 4 - 6 (not in 3-)
Chrome 1 - 45
Firefox 17 - 21 (not in 16-)
Rekonq 0.7.0 - 0.8.0
Not supported in Konqueror 4.7.4
Be careful with your minifier, though. It tends to remove comments. For the YUI compressor, a comment starting with /*! (like the one I used) will be preserved.
I think a real solution would be to use CoffeeScript.
ES6 UPDATE: You could use backtick instead of creating a function with a comment and running toString on the comment. The regex would need to be updated to only strip spaces. You could also have a string prototype method for doing this:
let foo = `
bar loves cake
baz loves beer
beer loves people
`.removeIndentation()
Someone should write this .removeIndentation string method... ;)

You can do this...
var string = 'This is\n' +
'a multiline\n' +
'string';

I came up with this very jimmy rigged method of a multi lined string. Since converting a function into a string also returns any comments inside the function you can use the comments as your string using a multilined comment /**/. You just have to trim off the ends and you have your string.
var myString = function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
alert(myString)

I'm surprised I didn't see this, because it works everywhere I've tested it and is very useful for e.g. templates:
<script type="bogus" id="multi">
My
multiline
string
</script>
<script>
alert($('#multi').html());
</script>
Does anybody know of an environment where there is HTML but it doesn't work?

I solved this by outputting a div, making it hidden, and calling the div id by jQuery when I needed it.
e.g.
<div id="UniqueID" style="display:none;">
Strings
On
Multiple
Lines
Here
</div>
Then when I need to get the string, I just use the following jQuery:
$('#UniqueID').html();
Which returns my text on multiple lines. If I call
alert($('#UniqueID').html());
I get:

There are multiple ways to achieve this
1. Slash concatenation
var MultiLine= '1\
2\
3\
4\
5\
6\
7\
8\
9';
2. regular concatenation
var MultiLine = '1'
+'2'
+'3'
+'4'
+'5';
3. Array Join concatenation
var MultiLine = [
'1',
'2',
'3',
'4',
'5'
].join('');
Performance wise, Slash concatenation (first one) is the fastest.
Refer this test case for more details regarding the performance
Update:
With the ES2015, we can take advantage of its Template strings feature. With it, we just need to use back-ticks for creating multi line strings
Example:
`<h1>{{title}}</h1>
<h2>{{hero.name}} details!</h2>
<div><label>id: </label>{{hero.id}}</div>
<div><label>name: </label>{{hero.name}}</div>
`

Using script tags:
add a <script>...</script> block containing your multiline text into head tag;
get your multiline text as is... (watch out for text encoding: UTF-8, ASCII)
<script>
// pure javascript
var text = document.getElementById("mySoapMessage").innerHTML ;
// using JQuery's document ready for safety
$(document).ready(function() {
var text = $("#mySoapMessage").html();
});
</script>
<script id="mySoapMessage" type="text/plain">
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:typ="...">
<soapenv:Header/>
<soapenv:Body>
<typ:getConvocadosElement>
...
</typ:getConvocadosElement>
</soapenv:Body>
</soapenv:Envelope>
<!-- this comment will be present on your string -->
//uh-oh, javascript comments... SOAP request will fail
</script>

I like this syntax and indendation:
string = 'my long string...\n'
+ 'continue here\n'
+ 'and here.';
(but actually can't be considered as multiline string)

Downvoters: This code is supplied for information only.
This has been tested in Fx 19 and Chrome 24 on Mac
DEMO
var new_comment; /*<<<EOF
<li class="photobooth-comment">
<span class="username">
You:
</span>
<span class="comment-text">
$text
</span>
#<span class="comment-time">
2d
</span> ago
</li>
EOF*/
// note the script tag here is hardcoded as the FIRST tag
new_comment=document.currentScript.innerHTML.split("EOF")[1];
document.querySelector("ul").innerHTML=new_comment.replace('$text','This is a dynamically created text');
<ul></ul>

A simple way to print multiline strings in JavaScript is by using template literals(template strings) denoted by backticks (` `). you can also use variables inside a template string-like (` name is ${value} `)
You can also
const value = `multiline`
const text = `This is a
${value}
string in js`;
console.log(text);

There's this library that makes it beautiful:
https://github.com/sindresorhus/multiline
Before
var str = '' +
'<!doctype html>' +
'<html>' +
' <body>' +
' <h1>❤ unicorns</h1>' +
' </body>' +
'</html>' +
'';
After
var str = multiline(function(){/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/});

Found a lot of over engineered answers here.
The two best answers in my opinion were:
1:
let str = `Multiline string.
foo.
bar.`
which eventually logs:
Multiline string.
foo.
bar.
2:
let str = `Multiline string.
foo.
bar.`
That logs it correctly but it's ugly in the script file if str is nested inside functions / objects etc...:
Multiline string.
foo.
bar.
My really simple answer with regex which logs the str correctly:
let str = `Multiline string.
foo.
bar.`.replace(/\n +/g, '\n');
Please note that it is not the perfect solution but it works if you are sure that after the new line (\n) at least one space will come (+ means at least one occurrence). It also will work with * (zero or more).
You can be more explicit and use {n,} which means at least n occurrences.

The equivalent in javascript is:
var text = `
This
Is
A
Multiline
String
`;
Here's the specification. See browser support at the bottom of this page. Here are some examples too.

This works in IE, Safari, Chrome and Firefox:
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
<div class="crazy_idea" thorn_in_my_side='<table border="0">
<tr>
<td ><span class="mlayouttablecellsdynamic">PACKAGE price $65.00</span></td>
</tr>
</table>'></div>
<script type="text/javascript">
alert($(".crazy_idea").attr("thorn_in_my_side"));
</script>

to sum up, I have tried 2 approaches listed here in user javascript programming (Opera 11.01):
this one didn't work: Creating multiline strings in JavaScript
this worked fairly well, I have also figured out how to make it look good in Notepad++ source view: Creating multiline strings in JavaScript
So I recommend the working approach for Opera user JS users. Unlike what the author was saying:
It doesn't work on firefox or opera; only on IE, chrome and safari.
It DOES work in Opera 11. At least in user JS scripts. Too bad I can't comment on individual answers or upvote the answer, I'd do it immediately. If possible, someone with higher privileges please do it for me.

Exact
Ruby produce: "This\nIs\nA\nMultiline\nString\n" - below JS produce exact same string
text = `This
Is
A
Multiline
String
`
// TEST
console.log(JSON.stringify(text));
console.log(text);
This is improvement to Lonnie Best answer because new-line characters in his answer are not exactly the same positions as in ruby output

My extension to https://stackoverflow.com/a/15558082/80404.
It expects comment in a form /*! any multiline comment */ where symbol ! is used to prevent removing by minification (at least for YUI compressor)
Function.prototype.extractComment = function() {
var startComment = "/*!";
var endComment = "*/";
var str = this.toString();
var start = str.indexOf(startComment);
var end = str.lastIndexOf(endComment);
return str.slice(start + startComment.length, -(str.length - end));
};
Example:
var tmpl = function() { /*!
<div class="navbar-collapse collapse">
<ul class="nav navbar-nav">
</ul>
</div>
*/}.extractComment();

Updated for 2015: it's six years later now: most people use a module loader, and the main module systems each have ways of loading templates. It's not inline, but the most common type of multiline string are templates, and templates should generally be kept out of JS anyway.
require.js: 'require text'.
Using require.js 'text' plugin, with a multiline template in template.html
var template = require('text!template.html')
NPM/browserify: the 'brfs' module
Browserify uses a 'brfs' module to load text files. This will actually build your template into your bundled HTML.
var fs = require("fs");
var template = fs.readFileSync(template.html', 'utf8');
Easy.

If you're willing to use the escaped newlines, they can be used nicely. It looks like a document with a page border.

Easiest way to make multiline strings in Javascrips is with the use of backticks ( `` ). This allows you to create multiline strings in which you can insert variables with ${variableName}.
Example:
let name = 'Willem';
let age = 26;
let multilineString = `
my name is: ${name}
my age is: ${age}
`;
console.log(multilineString);
compatibility :
It was introduces in ES6//es2015
It is now natively supported by all major browser vendors (except internet explorer)
Check exact compatibility in Mozilla docs here

The ES6 way of doing it would be by using template literals:
const str = `This
is
a
multiline text`;
console.log(str);
More reference here

You can use TypeScript (JavaScript SuperSet), it supports multiline strings, and transpiles back down to pure JavaScript without overhead:
var templates = {
myString: `this is
a multiline
string`
}
alert(templates.myString);
If you'd want to accomplish the same with plain JavaScript:
var templates =
{
myString: function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
}
alert(templates.myString)
Note that the iPad/Safari does not support 'functionName.toString()'
If you have a lot of legacy code, you can also use the plain JavaScript variant in TypeScript (for cleanup purposes):
interface externTemplates
{
myString:string;
}
declare var templates:externTemplates;
alert(templates.myString)
and you can use the multiline-string object from the plain JavaScript variant, where you put the templates into another file (which you can merge in the bundle).
You can try TypeScript at
http://www.typescriptlang.org/Playground

ES6 allows you to use a backtick to specify a string on multiple lines. It's called a Template Literal. Like this:
var multilineString = `One line of text
second line of text
third line of text
fourth line of text`;
Using the backtick works in NodeJS, and it's supported by Chrome, Firefox, Edge, Safari, and Opera.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

Also do note that, when extending string over multiple lines using forward backslash at end of each line, any extra characters (mostly spaces, tabs and comments added by mistake) after forward backslash will cause unexpected character error, which i took an hour to find out
var string = "line1\ // comment, space or tabs here raise error
line2";

Please for the love of the internet use string concatenation and opt not to use ES6 solutions for this. ES6 is NOT supported all across the board, much like CSS3 and certain browsers being slow to adapt to the CSS3 movement. Use plain ol' JavaScript, your end users will thank you.
Example:
var str = "This world is neither flat nor round. "+
"Once was lost will be found";

You can use tagged templates to make sure you get the desired output.
For example:
// Merging multiple whitespaces and trimming the output
const t = (strings) => { return strings.map((s) => s.replace(/\s+/g, ' ')).join("").trim() }
console.log(t`
This
Is
A
Multiline
String
`);
// Output: 'This Is A Multiline String'
// Similar but keeping whitespaces:
const tW = (strings) => { return strings.map((s) => s.replace(/\s+/g, '\n')).join("").trim() }
console.log(tW`
This
Is
A
Multiline
String
`);
// Output: 'This\nIs\nA\nMultiline\nString'

Multiline string with variables
var x = 1
string = string + `<label class="container">
<p>${x}</p>
</label>`;

Uncaught SyntaxError: Invalid or unexpected token in jquery [duplicate]

I have the following code in Ruby. I want to convert this code into JavaScript. What is the equivalent code in JS?
text = <<"HERE"
This
Is
A
Multiline
String
HERE

Update:
ECMAScript 6 (ES6) introduces a new type of literal, namely template literals. They have many features, variable interpolation among others, but most importantly for this question, they can be multiline.
A template literal is delimited by backticks:
var html = `
<div>
<span>Some HTML here</span>
</div>
`;
(Note: I'm not advocating to use HTML in strings)
Browser support is OK, but you can use transpilers to be more compatible.
Original ES5 answer:
Javascript doesn't have a here-document syntax. You can escape the literal newline, however, which comes close:
"foo \
bar"

ES6 Update:
As the first answer mentions, with ES6/Babel, you can now create multi-line strings simply by using backticks:
const htmlString = `Say hello to
multi-line
strings!`;
Interpolating variables is a popular new feature that comes with back-tick delimited strings:
const htmlString = `${user.name} liked your post about strings`;
This just transpiles down to concatenation:
user.name + ' liked your post about strings'
Original ES5 answer:
Google's JavaScript style guide recommends to use string concatenation instead of escaping newlines:
Do not do this:
var myString = 'A rather long string of English text, an error message \
actually that just keeps going and going -- an error \
message to make the Energizer bunny blush (right through \
those Schwarzenegger shades)! Where was I? Oh yes, \
you\'ve got an error and all the extraneous whitespace is \
just gravy. Have a nice day.';
The whitespace at the beginning of each line can't be safely stripped at compile time; whitespace after the slash will result in tricky errors; and while most script engines support this, it is not part of ECMAScript.
Use string concatenation instead:
var myString = 'A rather long string of English text, an error message ' +
'actually that just keeps going and going -- an error ' +
'message to make the Energizer bunny blush (right through ' +
'those Schwarzenegger shades)! Where was I? Oh yes, ' +
'you\'ve got an error and all the extraneous whitespace is ' +
'just gravy. Have a nice day.';

the pattern text = <<"HERE" This Is A Multiline String HERE is not available in js (I remember using it much in my good old Perl days).
To keep oversight with complex or long multiline strings I sometimes use an array pattern:
var myString =
['<div id="someId">',
'some content<br />',
'someRefTxt',
'</div>'
].join('\n');
or the pattern anonymous already showed (escape newline), which can be an ugly block in your code:
var myString =
'<div id="someId"> \
some content<br /> \
someRefTxt \
</div>';
Here's another weird but working 'trick'1:
var myString = (function () {/*
<div id="someId">
some content<br />
someRefTxt
</div>
*/}).toString().match(/[^]*\/\*([^]*)\*\/\}$/)[1];
external edit: jsfiddle
ES20xx supports spanning strings over multiple lines using template strings:
let str = `This is a text
with multiple lines.
Escapes are interpreted,
\n is a newline.`;
let str = String.raw`This is a text
with multiple lines.
Escapes are not interpreted,
\n is not a newline.`;
1 Note: this will be lost after minifying/obfuscating your code

You can have multiline strings in pure JavaScript.
This method is based on the serialization of functions, which is defined to be implementation-dependent. It does work in the most browsers (see below), but there's no guarantee that it will still work in the future, so do not rely on it.
Using the following function:
function hereDoc(f) {
return f.toString().
replace(/^[^\/]+\/\*!?/, '').
replace(/\*\/[^\/]+$/, '');
}
You can have here-documents like this:
var tennysonQuote = hereDoc(function() {/*!
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die
*/});
The method has successfully been tested in the following browsers (not mentioned = not tested):
IE 4 - 10
Opera 9.50 - 12 (not in 9-)
Safari 4 - 6 (not in 3-)
Chrome 1 - 45
Firefox 17 - 21 (not in 16-)
Rekonq 0.7.0 - 0.8.0
Not supported in Konqueror 4.7.4
Be careful with your minifier, though. It tends to remove comments. For the YUI compressor, a comment starting with /*! (like the one I used) will be preserved.
I think a real solution would be to use CoffeeScript.
ES6 UPDATE: You could use backtick instead of creating a function with a comment and running toString on the comment. The regex would need to be updated to only strip spaces. You could also have a string prototype method for doing this:
let foo = `
bar loves cake
baz loves beer
beer loves people
`.removeIndentation()
Someone should write this .removeIndentation string method... ;)

You can do this...
var string = 'This is\n' +
'a multiline\n' +
'string';

I came up with this very jimmy rigged method of a multi lined string. Since converting a function into a string also returns any comments inside the function you can use the comments as your string using a multilined comment /**/. You just have to trim off the ends and you have your string.
var myString = function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
alert(myString)

I'm surprised I didn't see this, because it works everywhere I've tested it and is very useful for e.g. templates:
<script type="bogus" id="multi">
My
multiline
string
</script>
<script>
alert($('#multi').html());
</script>
Does anybody know of an environment where there is HTML but it doesn't work?

I solved this by outputting a div, making it hidden, and calling the div id by jQuery when I needed it.
e.g.
<div id="UniqueID" style="display:none;">
Strings
On
Multiple
Lines
Here
</div>
Then when I need to get the string, I just use the following jQuery:
$('#UniqueID').html();
Which returns my text on multiple lines. If I call
alert($('#UniqueID').html());
I get:

There are multiple ways to achieve this
1. Slash concatenation
var MultiLine= '1\
2\
3\
4\
5\
6\
7\
8\
9';
2. regular concatenation
var MultiLine = '1'
+'2'
+'3'
+'4'
+'5';
3. Array Join concatenation
var MultiLine = [
'1',
'2',
'3',
'4',
'5'
].join('');
Performance wise, Slash concatenation (first one) is the fastest.
Refer this test case for more details regarding the performance
Update:
With the ES2015, we can take advantage of its Template strings feature. With it, we just need to use back-ticks for creating multi line strings
Example:
`<h1>{{title}}</h1>
<h2>{{hero.name}} details!</h2>
<div><label>id: </label>{{hero.id}}</div>
<div><label>name: </label>{{hero.name}}</div>
`

Using script tags:
add a <script>...</script> block containing your multiline text into head tag;
get your multiline text as is... (watch out for text encoding: UTF-8, ASCII)
<script>
// pure javascript
var text = document.getElementById("mySoapMessage").innerHTML ;
// using JQuery's document ready for safety
$(document).ready(function() {
var text = $("#mySoapMessage").html();
});
</script>
<script id="mySoapMessage" type="text/plain">
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:typ="...">
<soapenv:Header/>
<soapenv:Body>
<typ:getConvocadosElement>
...
</typ:getConvocadosElement>
</soapenv:Body>
</soapenv:Envelope>
<!-- this comment will be present on your string -->
//uh-oh, javascript comments... SOAP request will fail
</script>

I like this syntax and indendation:
string = 'my long string...\n'
+ 'continue here\n'
+ 'and here.';
(but actually can't be considered as multiline string)

Downvoters: This code is supplied for information only.
This has been tested in Fx 19 and Chrome 24 on Mac
DEMO
var new_comment; /*<<<EOF
<li class="photobooth-comment">
<span class="username">
You:
</span>
<span class="comment-text">
$text
</span>
#<span class="comment-time">
2d
</span> ago
</li>
EOF*/
// note the script tag here is hardcoded as the FIRST tag
new_comment=document.currentScript.innerHTML.split("EOF")[1];
document.querySelector("ul").innerHTML=new_comment.replace('$text','This is a dynamically created text');
<ul></ul>

A simple way to print multiline strings in JavaScript is by using template literals(template strings) denoted by backticks (` `). you can also use variables inside a template string-like (` name is ${value} `)
You can also
const value = `multiline`
const text = `This is a
${value}
string in js`;
console.log(text);

There's this library that makes it beautiful:
https://github.com/sindresorhus/multiline
Before
var str = '' +
'<!doctype html>' +
'<html>' +
' <body>' +
' <h1>❤ unicorns</h1>' +
' </body>' +
'</html>' +
'';
After
var str = multiline(function(){/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/});

Found a lot of over engineered answers here.
The two best answers in my opinion were:
1:
let str = `Multiline string.
foo.
bar.`
which eventually logs:
Multiline string.
foo.
bar.
2:
let str = `Multiline string.
foo.
bar.`
That logs it correctly but it's ugly in the script file if str is nested inside functions / objects etc...:
Multiline string.
foo.
bar.
My really simple answer with regex which logs the str correctly:
let str = `Multiline string.
foo.
bar.`.replace(/\n +/g, '\n');
Please note that it is not the perfect solution but it works if you are sure that after the new line (\n) at least one space will come (+ means at least one occurrence). It also will work with * (zero or more).
You can be more explicit and use {n,} which means at least n occurrences.

The equivalent in javascript is:
var text = `
This
Is
A
Multiline
String
`;
Here's the specification. See browser support at the bottom of this page. Here are some examples too.

This works in IE, Safari, Chrome and Firefox:
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
<div class="crazy_idea" thorn_in_my_side='<table border="0">
<tr>
<td ><span class="mlayouttablecellsdynamic">PACKAGE price $65.00</span></td>
</tr>
</table>'></div>
<script type="text/javascript">
alert($(".crazy_idea").attr("thorn_in_my_side"));
</script>

to sum up, I have tried 2 approaches listed here in user javascript programming (Opera 11.01):
this one didn't work: Creating multiline strings in JavaScript
this worked fairly well, I have also figured out how to make it look good in Notepad++ source view: Creating multiline strings in JavaScript
So I recommend the working approach for Opera user JS users. Unlike what the author was saying:
It doesn't work on firefox or opera; only on IE, chrome and safari.
It DOES work in Opera 11. At least in user JS scripts. Too bad I can't comment on individual answers or upvote the answer, I'd do it immediately. If possible, someone with higher privileges please do it for me.

Exact
Ruby produce: "This\nIs\nA\nMultiline\nString\n" - below JS produce exact same string
text = `This
Is
A
Multiline
String
`
// TEST
console.log(JSON.stringify(text));
console.log(text);
This is improvement to Lonnie Best answer because new-line characters in his answer are not exactly the same positions as in ruby output

My extension to https://stackoverflow.com/a/15558082/80404.
It expects comment in a form /*! any multiline comment */ where symbol ! is used to prevent removing by minification (at least for YUI compressor)
Function.prototype.extractComment = function() {
var startComment = "/*!";
var endComment = "*/";
var str = this.toString();
var start = str.indexOf(startComment);
var end = str.lastIndexOf(endComment);
return str.slice(start + startComment.length, -(str.length - end));
};
Example:
var tmpl = function() { /*!
<div class="navbar-collapse collapse">
<ul class="nav navbar-nav">
</ul>
</div>
*/}.extractComment();

Updated for 2015: it's six years later now: most people use a module loader, and the main module systems each have ways of loading templates. It's not inline, but the most common type of multiline string are templates, and templates should generally be kept out of JS anyway.
require.js: 'require text'.
Using require.js 'text' plugin, with a multiline template in template.html
var template = require('text!template.html')
NPM/browserify: the 'brfs' module
Browserify uses a 'brfs' module to load text files. This will actually build your template into your bundled HTML.
var fs = require("fs");
var template = fs.readFileSync(template.html', 'utf8');
Easy.

If you're willing to use the escaped newlines, they can be used nicely. It looks like a document with a page border.

Easiest way to make multiline strings in Javascrips is with the use of backticks ( `` ). This allows you to create multiline strings in which you can insert variables with ${variableName}.
Example:
let name = 'Willem';
let age = 26;
let multilineString = `
my name is: ${name}
my age is: ${age}
`;
console.log(multilineString);
compatibility :
It was introduces in ES6//es2015
It is now natively supported by all major browser vendors (except internet explorer)
Check exact compatibility in Mozilla docs here

The ES6 way of doing it would be by using template literals:
const str = `This
is
a
multiline text`;
console.log(str);
More reference here

You can use TypeScript (JavaScript SuperSet), it supports multiline strings, and transpiles back down to pure JavaScript without overhead:
var templates = {
myString: `this is
a multiline
string`
}
alert(templates.myString);
If you'd want to accomplish the same with plain JavaScript:
var templates =
{
myString: function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
}
alert(templates.myString)
Note that the iPad/Safari does not support 'functionName.toString()'
If you have a lot of legacy code, you can also use the plain JavaScript variant in TypeScript (for cleanup purposes):
interface externTemplates
{
myString:string;
}
declare var templates:externTemplates;
alert(templates.myString)
and you can use the multiline-string object from the plain JavaScript variant, where you put the templates into another file (which you can merge in the bundle).
You can try TypeScript at
http://www.typescriptlang.org/Playground

ES6 allows you to use a backtick to specify a string on multiple lines. It's called a Template Literal. Like this:
var multilineString = `One line of text
second line of text
third line of text
fourth line of text`;
Using the backtick works in NodeJS, and it's supported by Chrome, Firefox, Edge, Safari, and Opera.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

Also do note that, when extending string over multiple lines using forward backslash at end of each line, any extra characters (mostly spaces, tabs and comments added by mistake) after forward backslash will cause unexpected character error, which i took an hour to find out
var string = "line1\ // comment, space or tabs here raise error
line2";

Please for the love of the internet use string concatenation and opt not to use ES6 solutions for this. ES6 is NOT supported all across the board, much like CSS3 and certain browsers being slow to adapt to the CSS3 movement. Use plain ol' JavaScript, your end users will thank you.
Example:
var str = "This world is neither flat nor round. "+
"Once was lost will be found";

You can use tagged templates to make sure you get the desired output.
For example:
// Merging multiple whitespaces and trimming the output
const t = (strings) => { return strings.map((s) => s.replace(/\s+/g, ' ')).join("").trim() }
console.log(t`
This
Is
A
Multiline
String
`);
// Output: 'This Is A Multiline String'
// Similar but keeping whitespaces:
const tW = (strings) => { return strings.map((s) => s.replace(/\s+/g, '\n')).join("").trim() }
console.log(tW`
This
Is
A
Multiline
String
`);
// Output: 'This\nIs\nA\nMultiline\nString'

Multiline string with variables
var x = 1
string = string + `<label class="container">
<p>${x}</p>
</label>`;

Is there an alternative to template literals in Internet Explorer? [duplicate]

I have the following code in Ruby. I want to convert this code into JavaScript. What is the equivalent code in JS?
text = <<"HERE"
This
Is
A
Multiline
String
HERE

Update:
ECMAScript 6 (ES6) introduces a new type of literal, namely template literals. They have many features, variable interpolation among others, but most importantly for this question, they can be multiline.
A template literal is delimited by backticks:
var html = `
<div>
<span>Some HTML here</span>
</div>
`;
(Note: I'm not advocating to use HTML in strings)
Browser support is OK, but you can use transpilers to be more compatible.
Original ES5 answer:
Javascript doesn't have a here-document syntax. You can escape the literal newline, however, which comes close:
"foo \
bar"

ES6 Update:
As the first answer mentions, with ES6/Babel, you can now create multi-line strings simply by using backticks:
const htmlString = `Say hello to
multi-line
strings!`;
Interpolating variables is a popular new feature that comes with back-tick delimited strings:
const htmlString = `${user.name} liked your post about strings`;
This just transpiles down to concatenation:
user.name + ' liked your post about strings'
Original ES5 answer:
Google's JavaScript style guide recommends to use string concatenation instead of escaping newlines:
Do not do this:
var myString = 'A rather long string of English text, an error message \
actually that just keeps going and going -- an error \
message to make the Energizer bunny blush (right through \
those Schwarzenegger shades)! Where was I? Oh yes, \
you\'ve got an error and all the extraneous whitespace is \
just gravy. Have a nice day.';
The whitespace at the beginning of each line can't be safely stripped at compile time; whitespace after the slash will result in tricky errors; and while most script engines support this, it is not part of ECMAScript.
Use string concatenation instead:
var myString = 'A rather long string of English text, an error message ' +
'actually that just keeps going and going -- an error ' +
'message to make the Energizer bunny blush (right through ' +
'those Schwarzenegger shades)! Where was I? Oh yes, ' +
'you\'ve got an error and all the extraneous whitespace is ' +
'just gravy. Have a nice day.';

the pattern text = <<"HERE" This Is A Multiline String HERE is not available in js (I remember using it much in my good old Perl days).
To keep oversight with complex or long multiline strings I sometimes use an array pattern:
var myString =
['<div id="someId">',
'some content<br />',
'someRefTxt',
'</div>'
].join('\n');
or the pattern anonymous already showed (escape newline), which can be an ugly block in your code:
var myString =
'<div id="someId"> \
some content<br /> \
someRefTxt \
</div>';
Here's another weird but working 'trick'1:
var myString = (function () {/*
<div id="someId">
some content<br />
someRefTxt
</div>
*/}).toString().match(/[^]*\/\*([^]*)\*\/\}$/)[1];
external edit: jsfiddle
ES20xx supports spanning strings over multiple lines using template strings:
let str = `This is a text
with multiple lines.
Escapes are interpreted,
\n is a newline.`;
let str = String.raw`This is a text
with multiple lines.
Escapes are not interpreted,
\n is not a newline.`;
1 Note: this will be lost after minifying/obfuscating your code

You can have multiline strings in pure JavaScript.
This method is based on the serialization of functions, which is defined to be implementation-dependent. It does work in the most browsers (see below), but there's no guarantee that it will still work in the future, so do not rely on it.
Using the following function:
function hereDoc(f) {
return f.toString().
replace(/^[^\/]+\/\*!?/, '').
replace(/\*\/[^\/]+$/, '');
}
You can have here-documents like this:
var tennysonQuote = hereDoc(function() {/*!
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die
*/});
The method has successfully been tested in the following browsers (not mentioned = not tested):
IE 4 - 10
Opera 9.50 - 12 (not in 9-)
Safari 4 - 6 (not in 3-)
Chrome 1 - 45
Firefox 17 - 21 (not in 16-)
Rekonq 0.7.0 - 0.8.0
Not supported in Konqueror 4.7.4
Be careful with your minifier, though. It tends to remove comments. For the YUI compressor, a comment starting with /*! (like the one I used) will be preserved.
I think a real solution would be to use CoffeeScript.
ES6 UPDATE: You could use backtick instead of creating a function with a comment and running toString on the comment. The regex would need to be updated to only strip spaces. You could also have a string prototype method for doing this:
let foo = `
bar loves cake
baz loves beer
beer loves people
`.removeIndentation()
Someone should write this .removeIndentation string method... ;)

You can do this...
var string = 'This is\n' +
'a multiline\n' +
'string';

I came up with this very jimmy rigged method of a multi lined string. Since converting a function into a string also returns any comments inside the function you can use the comments as your string using a multilined comment /**/. You just have to trim off the ends and you have your string.
var myString = function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
alert(myString)

I'm surprised I didn't see this, because it works everywhere I've tested it and is very useful for e.g. templates:
<script type="bogus" id="multi">
My
multiline
string
</script>
<script>
alert($('#multi').html());
</script>
Does anybody know of an environment where there is HTML but it doesn't work?

I solved this by outputting a div, making it hidden, and calling the div id by jQuery when I needed it.
e.g.
<div id="UniqueID" style="display:none;">
Strings
On
Multiple
Lines
Here
</div>
Then when I need to get the string, I just use the following jQuery:
$('#UniqueID').html();
Which returns my text on multiple lines. If I call
alert($('#UniqueID').html());
I get:

There are multiple ways to achieve this
1. Slash concatenation
var MultiLine= '1\
2\
3\
4\
5\
6\
7\
8\
9';
2. regular concatenation
var MultiLine = '1'
+'2'
+'3'
+'4'
+'5';
3. Array Join concatenation
var MultiLine = [
'1',
'2',
'3',
'4',
'5'
].join('');
Performance wise, Slash concatenation (first one) is the fastest.
Refer this test case for more details regarding the performance
Update:
With the ES2015, we can take advantage of its Template strings feature. With it, we just need to use back-ticks for creating multi line strings
Example:
`<h1>{{title}}</h1>
<h2>{{hero.name}} details!</h2>
<div><label>id: </label>{{hero.id}}</div>
<div><label>name: </label>{{hero.name}}</div>
`

Using script tags:
add a <script>...</script> block containing your multiline text into head tag;
get your multiline text as is... (watch out for text encoding: UTF-8, ASCII)
<script>
// pure javascript
var text = document.getElementById("mySoapMessage").innerHTML ;
// using JQuery's document ready for safety
$(document).ready(function() {
var text = $("#mySoapMessage").html();
});
</script>
<script id="mySoapMessage" type="text/plain">
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:typ="...">
<soapenv:Header/>
<soapenv:Body>
<typ:getConvocadosElement>
...
</typ:getConvocadosElement>
</soapenv:Body>
</soapenv:Envelope>
<!-- this comment will be present on your string -->
//uh-oh, javascript comments... SOAP request will fail
</script>

I like this syntax and indendation:
string = 'my long string...\n'
+ 'continue here\n'
+ 'and here.';
(but actually can't be considered as multiline string)

Downvoters: This code is supplied for information only.
This has been tested in Fx 19 and Chrome 24 on Mac
DEMO
var new_comment; /*<<<EOF
<li class="photobooth-comment">
<span class="username">
You:
</span>
<span class="comment-text">
$text
</span>
#<span class="comment-time">
2d
</span> ago
</li>
EOF*/
// note the script tag here is hardcoded as the FIRST tag
new_comment=document.currentScript.innerHTML.split("EOF")[1];
document.querySelector("ul").innerHTML=new_comment.replace('$text','This is a dynamically created text');
<ul></ul>

A simple way to print multiline strings in JavaScript is by using template literals(template strings) denoted by backticks (` `). you can also use variables inside a template string-like (` name is ${value} `)
You can also
const value = `multiline`
const text = `This is a
${value}
string in js`;
console.log(text);

There's this library that makes it beautiful:
https://github.com/sindresorhus/multiline
Before
var str = '' +
'<!doctype html>' +
'<html>' +
' <body>' +
' <h1>❤ unicorns</h1>' +
' </body>' +
'</html>' +
'';
After
var str = multiline(function(){/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/});

Found a lot of over engineered answers here.
The two best answers in my opinion were:
1:
let str = `Multiline string.
foo.
bar.`
which eventually logs:
Multiline string.
foo.
bar.
2:
let str = `Multiline string.
foo.
bar.`
That logs it correctly but it's ugly in the script file if str is nested inside functions / objects etc...:
Multiline string.
foo.
bar.
My really simple answer with regex which logs the str correctly:
let str = `Multiline string.
foo.
bar.`.replace(/\n +/g, '\n');
Please note that it is not the perfect solution but it works if you are sure that after the new line (\n) at least one space will come (+ means at least one occurrence). It also will work with * (zero or more).
You can be more explicit and use {n,} which means at least n occurrences.

The equivalent in javascript is:
var text = `
This
Is
A
Multiline
String
`;
Here's the specification. See browser support at the bottom of this page. Here are some examples too.

This works in IE, Safari, Chrome and Firefox:
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
<div class="crazy_idea" thorn_in_my_side='<table border="0">
<tr>
<td ><span class="mlayouttablecellsdynamic">PACKAGE price $65.00</span></td>
</tr>
</table>'></div>
<script type="text/javascript">
alert($(".crazy_idea").attr("thorn_in_my_side"));
</script>

to sum up, I have tried 2 approaches listed here in user javascript programming (Opera 11.01):
this one didn't work: Creating multiline strings in JavaScript
this worked fairly well, I have also figured out how to make it look good in Notepad++ source view: Creating multiline strings in JavaScript
So I recommend the working approach for Opera user JS users. Unlike what the author was saying:
It doesn't work on firefox or opera; only on IE, chrome and safari.
It DOES work in Opera 11. At least in user JS scripts. Too bad I can't comment on individual answers or upvote the answer, I'd do it immediately. If possible, someone with higher privileges please do it for me.

Exact
Ruby produce: "This\nIs\nA\nMultiline\nString\n" - below JS produce exact same string
text = `This
Is
A
Multiline
String
`
// TEST
console.log(JSON.stringify(text));
console.log(text);
This is improvement to Lonnie Best answer because new-line characters in his answer are not exactly the same positions as in ruby output

My extension to https://stackoverflow.com/a/15558082/80404.
It expects comment in a form /*! any multiline comment */ where symbol ! is used to prevent removing by minification (at least for YUI compressor)
Function.prototype.extractComment = function() {
var startComment = "/*!";
var endComment = "*/";
var str = this.toString();
var start = str.indexOf(startComment);
var end = str.lastIndexOf(endComment);
return str.slice(start + startComment.length, -(str.length - end));
};
Example:
var tmpl = function() { /*!
<div class="navbar-collapse collapse">
<ul class="nav navbar-nav">
</ul>
</div>
*/}.extractComment();

Updated for 2015: it's six years later now: most people use a module loader, and the main module systems each have ways of loading templates. It's not inline, but the most common type of multiline string are templates, and templates should generally be kept out of JS anyway.
require.js: 'require text'.
Using require.js 'text' plugin, with a multiline template in template.html
var template = require('text!template.html')
NPM/browserify: the 'brfs' module
Browserify uses a 'brfs' module to load text files. This will actually build your template into your bundled HTML.
var fs = require("fs");
var template = fs.readFileSync(template.html', 'utf8');
Easy.

If you're willing to use the escaped newlines, they can be used nicely. It looks like a document with a page border.

Easiest way to make multiline strings in Javascrips is with the use of backticks ( `` ). This allows you to create multiline strings in which you can insert variables with ${variableName}.
Example:
let name = 'Willem';
let age = 26;
let multilineString = `
my name is: ${name}
my age is: ${age}
`;
console.log(multilineString);
compatibility :
It was introduces in ES6//es2015
It is now natively supported by all major browser vendors (except internet explorer)
Check exact compatibility in Mozilla docs here

The ES6 way of doing it would be by using template literals:
const str = `This
is
a
multiline text`;
console.log(str);
More reference here

You can use TypeScript (JavaScript SuperSet), it supports multiline strings, and transpiles back down to pure JavaScript without overhead:
var templates = {
myString: `this is
a multiline
string`
}
alert(templates.myString);
If you'd want to accomplish the same with plain JavaScript:
var templates =
{
myString: function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
}
alert(templates.myString)
Note that the iPad/Safari does not support 'functionName.toString()'
If you have a lot of legacy code, you can also use the plain JavaScript variant in TypeScript (for cleanup purposes):
interface externTemplates
{
myString:string;
}
declare var templates:externTemplates;
alert(templates.myString)
and you can use the multiline-string object from the plain JavaScript variant, where you put the templates into another file (which you can merge in the bundle).
You can try TypeScript at
http://www.typescriptlang.org/Playground

ES6 allows you to use a backtick to specify a string on multiple lines. It's called a Template Literal. Like this:
var multilineString = `One line of text
second line of text
third line of text
fourth line of text`;
Using the backtick works in NodeJS, and it's supported by Chrome, Firefox, Edge, Safari, and Opera.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

Also do note that, when extending string over multiple lines using forward backslash at end of each line, any extra characters (mostly spaces, tabs and comments added by mistake) after forward backslash will cause unexpected character error, which i took an hour to find out
var string = "line1\ // comment, space or tabs here raise error
line2";

Please for the love of the internet use string concatenation and opt not to use ES6 solutions for this. ES6 is NOT supported all across the board, much like CSS3 and certain browsers being slow to adapt to the CSS3 movement. Use plain ol' JavaScript, your end users will thank you.
Example:
var str = "This world is neither flat nor round. "+
"Once was lost will be found";

You can use tagged templates to make sure you get the desired output.
For example:
// Merging multiple whitespaces and trimming the output
const t = (strings) => { return strings.map((s) => s.replace(/\s+/g, ' ')).join("").trim() }
console.log(t`
This
Is
A
Multiline
String
`);
// Output: 'This Is A Multiline String'
// Similar but keeping whitespaces:
const tW = (strings) => { return strings.map((s) => s.replace(/\s+/g, '\n')).join("").trim() }
console.log(tW`
This
Is
A
Multiline
String
`);
// Output: 'This\nIs\nA\nMultiline\nString'

Multiline string with variables
var x = 1
string = string + `<label class="container">
<p>${x}</p>
</label>`;

What are the actual uses of ES6 Raw String Access?

What are the actual uses of String.raw Raw String Access introduced in ECMAScript 6?
// String.raw(callSite, ...substitutions)
function quux (strings, ...values) {
strings[0] === "foo\n"
strings[1] === "bar"
strings.raw[0] === "foo\\n"
strings.raw[1] === "bar"
values[0] === 42
}
quux `foo\n${ 42 }bar`
String.raw `foo\n${ 42 }bar` === "foo\\n42bar"
I went through the below docs.
http://es6-features.org/#RawStringAccess
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/template_strings
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/raw
http://www.2ality.com/2015/01/es6-strings.html
https://msdn.microsoft.com/en-us/library/dn889830(v=vs.94).aspx
The only the thing that I understand, is that it is used to get the raw string form of template strings and used for debugging the template string.
When this can be used in real time development? They were calling this a tag function. What does that mean?
What concrete use cases am I missing?

The best, and very nearly only, use case for String.raw I can think of is if you're trying to use something like Steven Levithan's XRegExp library that accepts text with significant backslashes. Using String.raw lets you write something semantically clear rather than having to think in terms of doubling your backslashes, just like you can in a regular expression literal in JavaScript itself.
For instance, suppose I'm doing maintenance on a site and I find this:
var isSingleUnicodeWord = /^\w+$/;
...which is meant to check if a string contains only "letters." Two problems: A) There are thousands of "word" characters across the realm of human language that \w doesn't recognize, because its definition is English-centric; and B) It includes _, which many (including the Unicode consortium) would argue is not a "letter."
So if we're using XRegExp on the site, since I know it supports \pL (\p for Unicode categories, and L for "letter"), I might quickly swap this in:
var isSingleUnicodeWord = XRegExp("^\pL+$"); // WRONG
Then I wonder why it didn't work, facepalm, and go back and escape that backslash, since it's being consumed by the string literal.
Easy enough in that simple regex, but in something complicated, remembering to double all those backslashes is a maintenance pain. (Just ask Java programmers trying to use Pattern.)
Enter String.raw:
let isSingleUnicodeWord = XRegExp(String.raw`^\pL+$`);
Example:
let isSingleUnicodeWord = XRegExp(String.raw`^\pL+$`); // L: Letter
console.log(isSingleUnicodeWord.test("Русский")); // true
console.log(isSingleUnicodeWord.test("日本語")); // true
console.log(isSingleUnicodeWord.test("العربية")); // true
console.log(isSingleUnicodeWord.test("foo bar")); // false
<script src="https://cdnjs.cloudflare.com/ajax/libs/xregexp/3.1.1/xregexp-all.min.js"></script>
Now I just kick back and write what I mean. I don't even really have to worry about ${...} constructs used in template literals to do substitution, because the odds of my wanting to apply a quantifier {...} to the end-of-line assertion ($) are...low. So I can happily use substitutions and still not worry about backslashes. Lovely.
Having said that, though, if I were doing it a lot, I'd probably want to write a function and use a tagged template instead of String.raw itself. But it's surprisingly awkward to do correctly:
// My one-time tag function
function xrex(strings, ...values) {
let raw = strings.raw;
let max = Math.max(raw.length, values.length);
let result = "";
for (let i = 0; i < max; ++i) {
if (i < raw.length) {
result += raw[i];
}
if (i < values.length) {
result += values[i];
}
}
console.log("Creating with:", result);
return XRegExp(result);
}
// Using it, with a couple of substitutions to prove to myself they work
let category = "L"; // L: Letter
let maybeEol = "$";
let isSingleUnicodeWord = xrex`^\p${category}+${maybeEol}`;
console.log(isSingleUnicodeWord.test("Русский")); // true
console.log(isSingleUnicodeWord.test("日本語")); // true
console.log(isSingleUnicodeWord.test("العربية")); // true
console.log(isSingleUnicodeWord.test("foo bar")); // false
<script src="https://cdnjs.cloudflare.com/ajax/libs/xregexp/3.1.1/xregexp-all.min.js"></script>
Maybe the hassle is worth it if you're using it in lots of places, but for a couple of quick ones, String.raw is the simpler option.

First, a few things:
Template strings is old name for template literals.
A tag is a function.
String.raw is a method.
String.raw `foo\n${ 42 }bar\` is a tagged template literal.
Template literals are basically fancy strings.
Template literals can interpolate.
Template literals can be multi-line without using \.
String.raw is required to escape the escape character \.
Try putting a string that contains a new-line character \n through a function that consumes newline character.
console.log("This\nis\nawesome"); // "This\nis\nawesome"
console.log(String.raw`This\nis\nawesome`); // "This\\nis\\nawesome"
If you are wondering, console.log is not one of them. But alert is. Try running these through http://learnharmony.org/ .
alert("This\nis\nawesome");
alert(String.raw`This\nis\nawesome`);
But wait, that's not the use of String.raw.
Possible uses of String.raw method:
To show string without interpretation of backslashed characters (\n, \t) etc.
To show code for the output. (As in example below)
To be used in regex without escaping \.
To print windows director/sub-directory locations without using \\ to much. (They use \ remember. Also, lol)
Here we can show output and code for it in single alert window:
alert("I printed This\nis\nawesome with " + Sring.raw`This\nis\nawesome`);
Though, it would have been great if It's main use could have been to get back the original string. Like:
var original = String.raw`This is awesome.`;
where original would have become: This\tis \tawesome.. This isn't the case sadly.
References:
http://exploringjs.com/es6/ch_template-literals.html
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/raw

Template strings can be useful in many situations which I will explain below. Considering this, the String.raw prevents escapes from being interpreted. This can be useful in any template string in which you want to contain the escape character but do not want to escape it. A simple example could be the following:
var templateWithBackslash = String.raw `someRegExp displayed in template /^\//`
There are a few things inside that are nice to note with template strings.
They can contain unescaped line breaks without problems.
They can contain "${}". Inside these curly braces the javascript is interpreted instead.
(Note: running these will output the result to your console [in browser dev tools])
Example using line breaks:
var myTemplate = `
<div class="myClass">
<pre>
My formatted text
with multiple lines
{
asdf: "and some pretty printed json"
}
</pre>
</div>
`
console.log(myTemplate)
If you wanted to do the above with a normal string in Javascript it would look like the following:
var myTemplate = "\
<div class="myClass">\
<pre>\
My formatted text\
with multiple lines\
{\
asdf: "and some pretty printed json"\
}\
</pre>\
</div>"
console.log(myTemplate)
You will notice the first probably looks much nicer (no need to escape line breaks).
For the second I will use the same template string but also insert the some pretty printed JSON.
var jsonObj = {asdf: "and some pretty printed json", deeper: {someDeep: "Some Deep Var"}}
var myTemplate = `
<div class="myClass">
<pre>
My formatted text
with multiple lines
${JSON.stringify(jsonObj, null, 2)}
</pre>
</div>
`
console.log(myTemplate)

In NodeJS it is extremely handy when it comes to filepath handling:
var fs=require('fs');
var s = String.raw`C:\Users\<username>\AppData\Roaming\SomeApp\someObject.json`;
var username = "bob"
s=s.replace("<username>",username)
fs.readFile(s,function(err,result){
if (err) throw error;
console.log(JSON.parse(result))
})
It improves readability of filepaths on Windows. \ is also a fairly common separator, so I can definitely see why it would be useful in general. However it is pretty stupid how \ still escapes `... So ultimately:
String.raw`C:\Users\` //#==> C:\Users\`
console.log(String.raw`C:\Users\`) //#==> SyntaxError: Unexpected end of input.

In addition to its use as a tag, String.raw is also useful in implementing new tag functions as a tool to do the interleaving that most people do with a weird loop. For example, compare:
function foo(strs, ...xs) {
let result = strs[0];
for (let i = 0; i < xs.length; ++i) {
result += useFoo(xs[i]) + strs[i + 1];
}
return result;
}
with
function foo(strs, ...xs) {
return String.raw({raw: strs}, ...xs.map(useFoo));
}

The Use
(Requisite knowledge: tstring §.)
Instead of:
console.log(`\\a\\b\\c\\n\\z\\x12\\xa9\\u1234\\u00A9\\u{1234}\\u{00A9}`);
.you can:
console.log(String.raw`\a\b\c\n\z\x12\xa9\u1234\u00A9\u{1234}\u{00A9}`);
"Escaping"
<\\u> is fine, yet <\u> needs "escaping", eg:
console.log(String.raw`abc${'\\u'}abc`);
.Dit <\\x>, <\x>,
<console.log(String.raw`abc${`\\x`}abc`)>;
.<\`>, <`>, <console.log(String.raw`abc${`\``}abc`)>;
.<\${>, <${&>, <console.log(String.raw`abc${`$\{`}abc`)>;
.<\\1> (till <\\7>), <\1>, <console.log(String.raw`abc${`\\1`}abc`)>;
.<\\>, endunit <\>, <console.log(String.raw`abc${`\\`}`)>.
Nb
There's also a new "latex" string. Cf §.

I've found it to be useful for testing
my RegExps. Say I have a RegExp which
should match end-of-line comments because
I want to remove them. BUT, it must not
match source-code for a regexp like /// .
If your code contains /// it is not the
start of an EOL comment but a RegExp, as
per the rules of JavaScript syntax.
I can test whether my RegExp in variable patEOLC
matches or doesn't /// with:
String.raw`/\//` .match (patEOLC)
In other words it is a way to let my
code "see" code the way it exists in
source-code, not the way it exists
in memory after it has been read
into memory from source-code, with
all backslashes removed.
It is a way to "escape escaping" but
without having to do it separately
for every backslash in a string, but
for all of them at the same time.
It is a way to say that in a given
(back-quoted) string backslash
shall behave just like any other
character, it has no special
meaning or interpretation.

What is the best and most semantic way to concatenate large amounts of string/text in javascript [duplicate]

I have the following code in Ruby. I want to convert this code into JavaScript. What is the equivalent code in JS?
text = <<"HERE"
This
Is
A
Multiline
String
HERE

Update:
ECMAScript 6 (ES6) introduces a new type of literal, namely template literals. They have many features, variable interpolation among others, but most importantly for this question, they can be multiline.
A template literal is delimited by backticks:
var html = `
<div>
<span>Some HTML here</span>
</div>
`;
(Note: I'm not advocating to use HTML in strings)
Browser support is OK, but you can use transpilers to be more compatible.
Original ES5 answer:
Javascript doesn't have a here-document syntax. You can escape the literal newline, however, which comes close:
"foo \
bar"

ES6 Update:
As the first answer mentions, with ES6/Babel, you can now create multi-line strings simply by using backticks:
const htmlString = `Say hello to
multi-line
strings!`;
Interpolating variables is a popular new feature that comes with back-tick delimited strings:
const htmlString = `${user.name} liked your post about strings`;
This just transpiles down to concatenation:
user.name + ' liked your post about strings'
Original ES5 answer:
Google's JavaScript style guide recommends to use string concatenation instead of escaping newlines:
Do not do this:
var myString = 'A rather long string of English text, an error message \
actually that just keeps going and going -- an error \
message to make the Energizer bunny blush (right through \
those Schwarzenegger shades)! Where was I? Oh yes, \
you\'ve got an error and all the extraneous whitespace is \
just gravy. Have a nice day.';
The whitespace at the beginning of each line can't be safely stripped at compile time; whitespace after the slash will result in tricky errors; and while most script engines support this, it is not part of ECMAScript.
Use string concatenation instead:
var myString = 'A rather long string of English text, an error message ' +
'actually that just keeps going and going -- an error ' +
'message to make the Energizer bunny blush (right through ' +
'those Schwarzenegger shades)! Where was I? Oh yes, ' +
'you\'ve got an error and all the extraneous whitespace is ' +
'just gravy. Have a nice day.';

the pattern text = <<"HERE" This Is A Multiline String HERE is not available in js (I remember using it much in my good old Perl days).
To keep oversight with complex or long multiline strings I sometimes use an array pattern:
var myString =
['<div id="someId">',
'some content<br />',
'someRefTxt',
'</div>'
].join('\n');
or the pattern anonymous already showed (escape newline), which can be an ugly block in your code:
var myString =
'<div id="someId"> \
some content<br /> \
someRefTxt \
</div>';
Here's another weird but working 'trick'1:
var myString = (function () {/*
<div id="someId">
some content<br />
someRefTxt
</div>
*/}).toString().match(/[^]*\/\*([^]*)\*\/\}$/)[1];
external edit: jsfiddle
ES20xx supports spanning strings over multiple lines using template strings:
let str = `This is a text
with multiple lines.
Escapes are interpreted,
\n is a newline.`;
let str = String.raw`This is a text
with multiple lines.
Escapes are not interpreted,
\n is not a newline.`;
1 Note: this will be lost after minifying/obfuscating your code

You can have multiline strings in pure JavaScript.
This method is based on the serialization of functions, which is defined to be implementation-dependent. It does work in the most browsers (see below), but there's no guarantee that it will still work in the future, so do not rely on it.
Using the following function:
function hereDoc(f) {
return f.toString().
replace(/^[^\/]+\/\*!?/, '').
replace(/\*\/[^\/]+$/, '');
}
You can have here-documents like this:
var tennysonQuote = hereDoc(function() {/*!
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die
*/});
The method has successfully been tested in the following browsers (not mentioned = not tested):
IE 4 - 10
Opera 9.50 - 12 (not in 9-)
Safari 4 - 6 (not in 3-)
Chrome 1 - 45
Firefox 17 - 21 (not in 16-)
Rekonq 0.7.0 - 0.8.0
Not supported in Konqueror 4.7.4
Be careful with your minifier, though. It tends to remove comments. For the YUI compressor, a comment starting with /*! (like the one I used) will be preserved.
I think a real solution would be to use CoffeeScript.
ES6 UPDATE: You could use backtick instead of creating a function with a comment and running toString on the comment. The regex would need to be updated to only strip spaces. You could also have a string prototype method for doing this:
let foo = `
bar loves cake
baz loves beer
beer loves people
`.removeIndentation()
Someone should write this .removeIndentation string method... ;)

You can do this...
var string = 'This is\n' +
'a multiline\n' +
'string';

I came up with this very jimmy rigged method of a multi lined string. Since converting a function into a string also returns any comments inside the function you can use the comments as your string using a multilined comment /**/. You just have to trim off the ends and you have your string.
var myString = function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
alert(myString)

I'm surprised I didn't see this, because it works everywhere I've tested it and is very useful for e.g. templates:
<script type="bogus" id="multi">
My
multiline
string
</script>
<script>
alert($('#multi').html());
</script>
Does anybody know of an environment where there is HTML but it doesn't work?

I solved this by outputting a div, making it hidden, and calling the div id by jQuery when I needed it.
e.g.
<div id="UniqueID" style="display:none;">
Strings
On
Multiple
Lines
Here
</div>
Then when I need to get the string, I just use the following jQuery:
$('#UniqueID').html();
Which returns my text on multiple lines. If I call
alert($('#UniqueID').html());
I get:

There are multiple ways to achieve this
1. Slash concatenation
var MultiLine= '1\
2\
3\
4\
5\
6\
7\
8\
9';
2. regular concatenation
var MultiLine = '1'
+'2'
+'3'
+'4'
+'5';
3. Array Join concatenation
var MultiLine = [
'1',
'2',
'3',
'4',
'5'
].join('');
Performance wise, Slash concatenation (first one) is the fastest.
Refer this test case for more details regarding the performance
Update:
With the ES2015, we can take advantage of its Template strings feature. With it, we just need to use back-ticks for creating multi line strings
Example:
`<h1>{{title}}</h1>
<h2>{{hero.name}} details!</h2>
<div><label>id: </label>{{hero.id}}</div>
<div><label>name: </label>{{hero.name}}</div>
`

Using script tags:
add a <script>...</script> block containing your multiline text into head tag;
get your multiline text as is... (watch out for text encoding: UTF-8, ASCII)
<script>
// pure javascript
var text = document.getElementById("mySoapMessage").innerHTML ;
// using JQuery's document ready for safety
$(document).ready(function() {
var text = $("#mySoapMessage").html();
});
</script>
<script id="mySoapMessage" type="text/plain">
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:typ="...">
<soapenv:Header/>
<soapenv:Body>
<typ:getConvocadosElement>
...
</typ:getConvocadosElement>
</soapenv:Body>
</soapenv:Envelope>
<!-- this comment will be present on your string -->
//uh-oh, javascript comments... SOAP request will fail
</script>

I like this syntax and indendation:
string = 'my long string...\n'
+ 'continue here\n'
+ 'and here.';
(but actually can't be considered as multiline string)

Downvoters: This code is supplied for information only.
This has been tested in Fx 19 and Chrome 24 on Mac
DEMO
var new_comment; /*<<<EOF
<li class="photobooth-comment">
<span class="username">
You:
</span>
<span class="comment-text">
$text
</span>
#<span class="comment-time">
2d
</span> ago
</li>
EOF*/
// note the script tag here is hardcoded as the FIRST tag
new_comment=document.currentScript.innerHTML.split("EOF")[1];
document.querySelector("ul").innerHTML=new_comment.replace('$text','This is a dynamically created text');
<ul></ul>

A simple way to print multiline strings in JavaScript is by using template literals(template strings) denoted by backticks (` `). you can also use variables inside a template string-like (` name is ${value} `)
You can also
const value = `multiline`
const text = `This is a
${value}
string in js`;
console.log(text);

There's this library that makes it beautiful:
https://github.com/sindresorhus/multiline
Before
var str = '' +
'<!doctype html>' +
'<html>' +
' <body>' +
' <h1>❤ unicorns</h1>' +
' </body>' +
'</html>' +
'';
After
var str = multiline(function(){/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/});

Found a lot of over engineered answers here.
The two best answers in my opinion were:
1:
let str = `Multiline string.
foo.
bar.`
which eventually logs:
Multiline string.
foo.
bar.
2:
let str = `Multiline string.
foo.
bar.`
That logs it correctly but it's ugly in the script file if str is nested inside functions / objects etc...:
Multiline string.
foo.
bar.
My really simple answer with regex which logs the str correctly:
let str = `Multiline string.
foo.
bar.`.replace(/\n +/g, '\n');
Please note that it is not the perfect solution but it works if you are sure that after the new line (\n) at least one space will come (+ means at least one occurrence). It also will work with * (zero or more).
You can be more explicit and use {n,} which means at least n occurrences.

The equivalent in javascript is:
var text = `
This
Is
A
Multiline
String
`;
Here's the specification. See browser support at the bottom of this page. Here are some examples too.

This works in IE, Safari, Chrome and Firefox:
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
<div class="crazy_idea" thorn_in_my_side='<table border="0">
<tr>
<td ><span class="mlayouttablecellsdynamic">PACKAGE price $65.00</span></td>
</tr>
</table>'></div>
<script type="text/javascript">
alert($(".crazy_idea").attr("thorn_in_my_side"));
</script>

to sum up, I have tried 2 approaches listed here in user javascript programming (Opera 11.01):
this one didn't work: Creating multiline strings in JavaScript
this worked fairly well, I have also figured out how to make it look good in Notepad++ source view: Creating multiline strings in JavaScript
So I recommend the working approach for Opera user JS users. Unlike what the author was saying:
It doesn't work on firefox or opera; only on IE, chrome and safari.
It DOES work in Opera 11. At least in user JS scripts. Too bad I can't comment on individual answers or upvote the answer, I'd do it immediately. If possible, someone with higher privileges please do it for me.

Exact
Ruby produce: "This\nIs\nA\nMultiline\nString\n" - below JS produce exact same string
text = `This
Is
A
Multiline
String
`
// TEST
console.log(JSON.stringify(text));
console.log(text);
This is improvement to Lonnie Best answer because new-line characters in his answer are not exactly the same positions as in ruby output

My extension to https://stackoverflow.com/a/15558082/80404.
It expects comment in a form /*! any multiline comment */ where symbol ! is used to prevent removing by minification (at least for YUI compressor)
Function.prototype.extractComment = function() {
var startComment = "/*!";
var endComment = "*/";
var str = this.toString();
var start = str.indexOf(startComment);
var end = str.lastIndexOf(endComment);
return str.slice(start + startComment.length, -(str.length - end));
};
Example:
var tmpl = function() { /*!
<div class="navbar-collapse collapse">
<ul class="nav navbar-nav">
</ul>
</div>
*/}.extractComment();

Updated for 2015: it's six years later now: most people use a module loader, and the main module systems each have ways of loading templates. It's not inline, but the most common type of multiline string are templates, and templates should generally be kept out of JS anyway.
require.js: 'require text'.
Using require.js 'text' plugin, with a multiline template in template.html
var template = require('text!template.html')
NPM/browserify: the 'brfs' module
Browserify uses a 'brfs' module to load text files. This will actually build your template into your bundled HTML.
var fs = require("fs");
var template = fs.readFileSync(template.html', 'utf8');
Easy.

If you're willing to use the escaped newlines, they can be used nicely. It looks like a document with a page border.

Easiest way to make multiline strings in Javascrips is with the use of backticks ( `` ). This allows you to create multiline strings in which you can insert variables with ${variableName}.
Example:
let name = 'Willem';
let age = 26;
let multilineString = `
my name is: ${name}
my age is: ${age}
`;
console.log(multilineString);
compatibility :
It was introduces in ES6//es2015
It is now natively supported by all major browser vendors (except internet explorer)
Check exact compatibility in Mozilla docs here

The ES6 way of doing it would be by using template literals:
const str = `This
is
a
multiline text`;
console.log(str);
More reference here

You can use TypeScript (JavaScript SuperSet), it supports multiline strings, and transpiles back down to pure JavaScript without overhead:
var templates = {
myString: `this is
a multiline
string`
}
alert(templates.myString);
If you'd want to accomplish the same with plain JavaScript:
var templates =
{
myString: function(){/*
This is some
awesome multi-lined
string using a comment
inside a function
returned as a string.
Enjoy the jimmy rigged code.
*/}.toString().slice(14,-3)
}
alert(templates.myString)
Note that the iPad/Safari does not support 'functionName.toString()'
If you have a lot of legacy code, you can also use the plain JavaScript variant in TypeScript (for cleanup purposes):
interface externTemplates
{
myString:string;
}
declare var templates:externTemplates;
alert(templates.myString)
and you can use the multiline-string object from the plain JavaScript variant, where you put the templates into another file (which you can merge in the bundle).
You can try TypeScript at
http://www.typescriptlang.org/Playground

ES6 allows you to use a backtick to specify a string on multiple lines. It's called a Template Literal. Like this:
var multilineString = `One line of text
second line of text
third line of text
fourth line of text`;
Using the backtick works in NodeJS, and it's supported by Chrome, Firefox, Edge, Safari, and Opera.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

Also do note that, when extending string over multiple lines using forward backslash at end of each line, any extra characters (mostly spaces, tabs and comments added by mistake) after forward backslash will cause unexpected character error, which i took an hour to find out
var string = "line1\ // comment, space or tabs here raise error
line2";

Please for the love of the internet use string concatenation and opt not to use ES6 solutions for this. ES6 is NOT supported all across the board, much like CSS3 and certain browsers being slow to adapt to the CSS3 movement. Use plain ol' JavaScript, your end users will thank you.
Example:
var str = "This world is neither flat nor round. "+
"Once was lost will be found";

You can use tagged templates to make sure you get the desired output.
For example:
// Merging multiple whitespaces and trimming the output
const t = (strings) => { return strings.map((s) => s.replace(/\s+/g, ' ')).join("").trim() }
console.log(t`
This
Is
A
Multiline
String
`);
// Output: 'This Is A Multiline String'
// Similar but keeping whitespaces:
const tW = (strings) => { return strings.map((s) => s.replace(/\s+/g, '\n')).join("").trim() }
console.log(tW`
This
Is
A
Multiline
String
`);
// Output: 'This\nIs\nA\nMultiline\nString'

Multiline string with variables
var x = 1
string = string + `<label class="container">
<p>${x}</p>
</label>`;