Develop Reference

JS Regex match word, but the word is dynamic [duplicate]

This question already has answers here:
How do you use a variable in a regular expression?
(27 answers)
Closed 2 years ago.
So for example:
function(input){
var testVar = input;
string = ...
string.replace(/ReGeX + testVar + ReGeX/, "replacement")
}
But this is of course not working :)
Is there any way to do this?

const regex = new RegExp(`ReGeX${testVar}ReGeX`);
...
string.replace(regex, "replacement");
Update
Per some of the comments, it's important to note that you may want to escape the variable if there is potential for malicious content (e.g. the variable comes from user input)
ES6 Update
In 2019, this would usually be written using a template string, and the above code has been updated. The original answer was:
var regex = new RegExp("ReGeX" + testVar + "ReGeX");
...
string.replace(regex, "replacement");

You can use the RegExp object:
var regexstring = "whatever";
var regexp = new RegExp(regexstring, "gi");
var str = "whateverTest";
var str2 = str.replace(regexp, "other");
document.write(str2);
Then you can construct regexstring in any way you want.
You can read more about it here.

To build a regular expression from a variable in JavaScript, you'll need to use the RegExp constructor with a string parameter.
function reg(input) {
var flags;
//could be any combination of 'g', 'i', and 'm'
flags = 'g';
return new RegExp('ReGeX' + input + 'ReGeX', flags);
}
of course, this is a very naive example. It assumes that input is has been properly escaped for a regular expression. If you're dealing with user-input, or simply want to make it more convenient to match special characters, you'll need to escape special characters:
function regexEscape(str) {
return str.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')
}
function reg(input) {
var flags;
//could be any combination of 'g', 'i', and 'm'
flags = 'g';
input = regexEscape(input);
return new RegExp('ReGeX' + input + 'ReGeX', flags);
}

You can create regular expressions in JS in one of two ways:
Using regular expression literal - /ab{2}/g
Using the regular expression constructor - new RegExp("ab{2}", "g") .
Regular expression literals are constant, and can not be used with variables. This could be achieved using the constructor. The stracture of the RegEx constructor is
new RegExp(regularExpressionString, modifiersString)
You can embed variables as part of the regularExpressionString. For example,
var pattern="cd"
var repeats=3
new RegExp(`${pattern}{${repeats}}`, "g")
This will match any appearance of the pattern cdcdcd.

if you're using es6 template literals are an option...
string.replace(new RegExp(`ReGeX${testVar}ReGeX`), "replacement")

You can always give regular expression as string, i.e. "ReGeX" + testVar + "ReGeX". You'll possibly have to escape some characters inside your string (e.g., double quote), but for most cases it's equivalent.
You can also use RegExp constructor to pass flags in (see the docs).

It's only necessary to prepare the string variable first and then convert it to the RegEx.
for example:
You want to add minLength and MaxLength with the variable to RegEx:
function getRegEx() {
const minLength = "5"; // for exapmle: min is 5
const maxLength = "12"; // for exapmle: man is 12
var regEx = "^.{" + minLength + ","+ maxLength +"}$"; // first we make a String variable of our RegEx
regEx = new RegExp(regEx, "g"); // now we convert it to RegEx
return regEx; // In the end, we return the RegEx
}
now if you change value of MaxLength or MinLength, It will change in all RegExs.
Hope to be useful. Also sorry about my English.

Here's an pretty useless function that return values wrapped by specific characters. :)
jsfiddle: https://jsfiddle.net/squadjot/43agwo6x/
function getValsWrappedIn(str,c1,c2){
var rg = new RegExp("(?<=\\"+c1+")(.*?)(?=\\"+c2+")","g");
return str.match(rg);
}
var exampleStr = "Something (5) or some time (19) or maybe a (thingy)";
var results = getValsWrappedIn(exampleStr,"(",")")
// Will return array ["5","19","thingy"]
console.log(results)

accepted answer doesn't work for me and doesn't follow MDN examples
see the 'Description' section in above link
I'd go with the following it's working for me:
let stringThatIsGoingToChange = 'findMe';
let flagsYouWant = 'gi' //simple string with flags
let dynamicRegExp = new RegExp(`${stringThatIsGoingToChange}`, flagsYouWant)
// that makes dynamicRegExp = /findMe/gi

Javascript regex error " /?/: nothing to repeat " It worked fine earlier [duplicate]

This question already has answers here:
What does the "Nothing to repeat" error mean when using a regex in javascript?
(7 answers)
Closed 4 years ago.
I'm trying to clear a string of any invalid characters to be set as a directory.
Tried a number of methods and this one eventually worked[custom encoding] but now it doesn't, it says "nothing to repeat" in the console. What does that mean? using Chrome.
Here's the code(using random string):
var someTitle = "wa?";
var cleanTitle = cleanTitle(someTitle);
function cleanTitle(title){
var obstructions = ['\\','/',':','*','?','"','<','>','|'];
var solutions = [92,47,58,42,63,34,60,62,124];
var encodedTitle = title;
for (var obstruction = 0; obstruction < obstructions.length; obstruction++){
var char = obstructions[obstruction];
if (encodedTitle.includes(char)){
var enCode = "__i!__"+solutions[obstruction]+"__!i__";
var rEx = new RegExp(char,"g");
encodedTitle = encodedTitle.replace(rEx,enCode);
}
}
console.log("CLEAN: "+title);
console.log("ENCODED: "+encodedTitle);
return encodedTitle;
}
Heres the error:
Uncaught SyntaxError: Invalid regular expression: /?/: Nothing to
repeat
It points to this line -> var rEx = new RegExp(char,"g");

You need to escape some characters when using them as literals in a regular expression. Among those are most of the characters you have in your array.
Given your function replaces the obstruction characters with their ASCII code (and some wrapping __i!__), I would suggest to make your function a bit more concise, by performing the replacement with one regular expression, and a callback passed to .replace():
function cleanTitle(title){
return title.replace(/[\\/:*?"<>|]/g, function (ch) {
return "__i!__"+ch.charCodeAt(0)+"__!i__";
});
}
var someTitle = "wh*r* is |his?";
var result = cleanTitle(someTitle);
console.log(result);
...and if you are in an ES6 compatible environment:
var cleanTitle = t=>t.replace(/[\\/:*?"<>|]/g, c=>"__i!__"+c.charCodeAt(0)+"__!i__");
var someTitle = "wh*r* is |his?";
var result = cleanTitle(someTitle);
console.log(result);

The ? is a regex modifier. When you want to look for it (and build a regex with it), you need to escape it.
That beeing said, a harmless unuseful escaping doesn't hurt (or makes your other search params useable, as there are many modifiers or reserved chars in it) your other search params. So go with
var char = '\\' + obstructions[obstruction];
to replace them all with a (for the regex) string representation

/?/ is not a valid regex. For it to be a regex, you need /\?/.
Regex here would be awkward, as most of the characters need escaping. Instead, consider using a literal string replacement until it is no longer found:
while( encodedTitle.indexOf(char) > -1) {
encodedTitle = encodedTitle.replace(char,enCode);
}

How can I do string replace in jquery [duplicate]

This question already has answers here:
How do I replace all occurrences of a string in JavaScript?
(78 answers)
Closed 6 years ago.
I have this code
$("#title").keyup(function(){
var titleval = $("#title").val();
var res = titleval.replace(" ", "-");
$("#newsurl").val(res);
});
to replace spaces into dash to get URL like this
wordone-wordtow-wordthree
but i have problem with this code it's just replace first space like this
wordone-wordtow wordthree
How can i solve this problem

You need to do a global match, you can do this with a regex
var res = titleval.replace(/\s/g, "-");
Though String.prototype.replace does support having flags passed, this is deprecated in firefox and already doesn't work in chrome/v8.

Alternate method (if regex is not mandatory) could be to split and join
var res = titleval.split(" ").join("-");
or
var res = titleval.split(/\s+/).join("-");

Use regex with global flag
titleval.replace(/\s/g, "-");

try like this:
$("#title").keyup(function(){
var titleval = $("#title").val();
var res = titleval.replace(/\s+/g, '-');
$("#newsurl").val(res);
});

Substituting Regex whitespace with JavaScript [duplicate]

This question already has answers here:
JavaScript RegExp: Different results: Built pattern using string & using regexp "literal"?
(2 answers)
Closed 8 years ago.
I'm well aware of the standard approach of using the RegExp object to match dynamic variables in JavaScript. However I'm having some difficulty with whitespacing.
The aim is that there can be 0 or more white spaces in between {{ or }}, and the dynamic variable name.
The behaviour I'm trying to mirror
var regex = /\{\{\s*name\s*\}\}/g;
var string = "Howdy, my name is {{ name}}";
string.replace(regex, "Chris")
// => "Howdy, my name is Chris"
My current code
var keyName = "name";
var regex = new RegExp("\{\{\s*"+keyName+"\s*\}\}", "g");
var string = "Howdy, my name is {{ name}}";
string.replace(regex, "Chris")
// => "Howdy, my name is {{ name}}"
Am I missing something? Thanks

You missed the escapes. Replace this:
new RegExp("\{\{\s*"+name+"\s*\}\}", "g");
With this:
new RegExp("\\{\\{\\s*"+name+"\\s*\\}\\}", "g");
You have to double escape the backslashes, once for the JS string, and once for the regex.
That's the reason behind the regex literal /.../ which you can't use here... Or, perhaps you could:
var regex = /\{\{\s*(\w+)\s*\}\}/g;
Capture everything, and filter out the results afterwards. The name is in the first captured group.
string.replace(regex, function(m, name) {
return "whatever " + name;
});

Your code would be,
> var keyName = "name";
> var regex = new RegExp("\\{\\{\\s*"+keyName+"\\s*\\}\\}", "g");
undefined
> var string = "Howdy, my name is {{ name}}";
undefined
> string.replace(regex, "Chris")
'Howdy, my name is Chris'
You need to include the variable which stores the value name in the RegExp pattern and also you need to escape \ one more time because the pattern was included within double quotes .

Javascript Regex: How to put a variable inside a regular expression? [duplicate]

This question already has answers here:
How do you use a variable in a regular expression?
(27 answers)
Closed 2 years ago.
So for example:
function(input){
var testVar = input;
string = ...
string.replace(/ReGeX + testVar + ReGeX/, "replacement")
}
But this is of course not working :)
Is there any way to do this?

const regex = new RegExp(`ReGeX${testVar}ReGeX`);
...
string.replace(regex, "replacement");
Update
Per some of the comments, it's important to note that you may want to escape the variable if there is potential for malicious content (e.g. the variable comes from user input)
ES6 Update
In 2019, this would usually be written using a template string, and the above code has been updated. The original answer was:
var regex = new RegExp("ReGeX" + testVar + "ReGeX");
...
string.replace(regex, "replacement");

You can use the RegExp object:
var regexstring = "whatever";
var regexp = new RegExp(regexstring, "gi");
var str = "whateverTest";
var str2 = str.replace(regexp, "other");
document.write(str2);
Then you can construct regexstring in any way you want.
You can read more about it here.

To build a regular expression from a variable in JavaScript, you'll need to use the RegExp constructor with a string parameter.
function reg(input) {
var flags;
//could be any combination of 'g', 'i', and 'm'
flags = 'g';
return new RegExp('ReGeX' + input + 'ReGeX', flags);
}
of course, this is a very naive example. It assumes that input is has been properly escaped for a regular expression. If you're dealing with user-input, or simply want to make it more convenient to match special characters, you'll need to escape special characters:
function regexEscape(str) {
return str.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')
}
function reg(input) {
var flags;
//could be any combination of 'g', 'i', and 'm'
flags = 'g';
input = regexEscape(input);
return new RegExp('ReGeX' + input + 'ReGeX', flags);
}

You can create regular expressions in JS in one of two ways:
Using regular expression literal - /ab{2}/g
Using the regular expression constructor - new RegExp("ab{2}", "g") .
Regular expression literals are constant, and can not be used with variables. This could be achieved using the constructor. The stracture of the RegEx constructor is
new RegExp(regularExpressionString, modifiersString)
You can embed variables as part of the regularExpressionString. For example,
var pattern="cd"
var repeats=3
new RegExp(`${pattern}{${repeats}}`, "g")
This will match any appearance of the pattern cdcdcd.

if you're using es6 template literals are an option...
string.replace(new RegExp(`ReGeX${testVar}ReGeX`), "replacement")

You can always give regular expression as string, i.e. "ReGeX" + testVar + "ReGeX". You'll possibly have to escape some characters inside your string (e.g., double quote), but for most cases it's equivalent.
You can also use RegExp constructor to pass flags in (see the docs).

It's only necessary to prepare the string variable first and then convert it to the RegEx.
for example:
You want to add minLength and MaxLength with the variable to RegEx:
function getRegEx() {
const minLength = "5"; // for exapmle: min is 5
const maxLength = "12"; // for exapmle: man is 12
var regEx = "^.{" + minLength + ","+ maxLength +"}$"; // first we make a String variable of our RegEx
regEx = new RegExp(regEx, "g"); // now we convert it to RegEx
return regEx; // In the end, we return the RegEx
}
now if you change value of MaxLength or MinLength, It will change in all RegExs.
Hope to be useful. Also sorry about my English.

Here's an pretty useless function that return values wrapped by specific characters. :)
jsfiddle: https://jsfiddle.net/squadjot/43agwo6x/
function getValsWrappedIn(str,c1,c2){
var rg = new RegExp("(?<=\\"+c1+")(.*?)(?=\\"+c2+")","g");
return str.match(rg);
}
var exampleStr = "Something (5) or some time (19) or maybe a (thingy)";
var results = getValsWrappedIn(exampleStr,"(",")")
// Will return array ["5","19","thingy"]
console.log(results)

accepted answer doesn't work for me and doesn't follow MDN examples
see the 'Description' section in above link
I'd go with the following it's working for me:
let stringThatIsGoingToChange = 'findMe';
let flagsYouWant = 'gi' //simple string with flags
let dynamicRegExp = new RegExp(`${stringThatIsGoingToChange}`, flagsYouWant)
// that makes dynamicRegExp = /findMe/gi