I have a string "messages.get.342" that I want to convert to "messages/get/342". Unfortunately, when I call "messages.get.342".replace('.', '/'), I get "messages/get.342". What gives?
You need to use a global replace with regex like this.
"messages.get.342".replace(/\./g, '/');
Edit:
You can also do it like this; it is a little longer but can be less confusing.
var myString = "messages/get/342";
var regex = new RegExp(/\./, "g");
myString = mystring.replace(regex, myString);
You have the following three options available to you with the javascript regex object:
i - case insensitive matching
g - global matching
m - multiline matching
You can use the other two options in replace of the g (/i or "i") or in combination with the g (/gi or "gi").
Use Regular Expression
"messages.get.342".replace(/\./g, '/')
You need to use a regular expression with the global flag to replace ALL instances of the period:
document.write("messages.get.342".replace(/\./g, '/'));
Do it globally:
"messages.get.342".replace(/\./g, '/')
The \. is an escaped period, and the slashes around it indicate a pattern match. You have to escape a literal period if you're doing a pattern match. The g means global, i.e., match and replace all occurrences, not just the first.
Don't use replace for strings. "messages.get.342".split('.').join('/') is recommended.
Related
<script>
var String = "1 Apple and 13 Oranges";
var regex = /[^\d]/g;
var regObj = new RegExp(regex);
document.write(String.replace(regObj,''));
</script>
And it works fine - return all the digits in the string.
However when I put quote marks around the regex like this:
var regex = "/[^\d]/g"; This doesn't work.
How can I turn a string to a working regex in this case?
Thanks
You can create regular expressions in two ways, using the regular expression literal notation, or RegExp constructor. It seems you have mixed up the two. :)
Here is the literal way:
var regex = /[^\d]/g;
In this case you don't have use quotes. / characters at the ends serve as the delimiters, and you specify the flags at the end.
Here is how to use the RegExp constructor, in which you pass the pattern and flags (optional) as string. When you use strings you have to escape any special characters inside it using a '\'.
Since the '\' (backslash) is a special character, you have to escape the backslash using another backslash if you use double quotes.
var regex = new RegExp("[^\\d]", "g");
Hope this makes sense.
As slash(\) has special meaning for strings (e.g. "\n","\t", etc...), you need to escape that simbol, when you are passing to regexp:
var regex = "[^\\d]";
Also expression flags (e.g. g,i,etc...) must be passed as separate parameter for RegExp.
So overall:
var regex = "[^\\d]";
var flags = "g";
var regObj = new RegExp(regex, flags);
i am trying
To convert: 'any string separated with blankspaces' into
'any-string-separated-with-blankspaces'
i am tying with .replace(' ','-') but it would only replace first... why? how can i replace all?
http://jsfiddle.net/7ycg3/
You need a regular expression for that
.replace(/\s/g,'-')
\s will replace any kind of white-space character. If you're strictly after a "normal" whitespace use
/ /g
instead.
You need to use a regular expression as the first parameter, using the /g modifier to make it replace all occurrences:
var replaced = input.replace(/ /g,'-');
If you want to replace any whitespace character instead of a literal space, you need to use \s instead of in the regex; and if you want to replace any number of consecutive spaces with one hyphen, then add + after the or \s.
It's not stated particularly clearly in the MDN docs for String.replace, but String.replace only does one replacement, unless the g flag is included in it, using a regular expression rather than a string:
To perform a global search and replace, either include the g switch in the regular expression or if the first parameter is a string, include g in the flags parameter.
(But be aware that the flags parameter is non-standard, as they also note there.)
Thus, you want tag.replace(/ /g,'-').
http://jsfiddle.net/7ycg3/1/
Use regex with /g modifier
Use /\s/g inplace of ' ' in your question
I am trying to build a regexp from static text plus a variable in javascript. Obviously I am missing something very basic, see comments in code below. Help is very much appreciated:
var test_string = "goodweather";
// One regexp we just set:
var regexp1 = /goodweather/;
// The other regexp we built from a variable + static text:
var regexp_part = "good";
var regexp2 = "\/" + regexp_part + "weather\/";
// These alerts now show the 2 regexp are completely identical:
alert (regexp1);
alert (regexp2);
// But one works, the other doesn't ??
if (test_string.match(regexp1))
alert ("This is displayed.");
if (test_string.match(regexp2))
alert ("This is not displayed.");
First, the answer to the question:
The other answers are nearly correct, but fail to consider what happens when the text to be matched contains a literal backslash, (i.e. when: regexp_part contains a literal backslash). For example, what happens when regexp_part equals: "C:\Windows"? In this case the suggested methods do not work as expected (The resulting regex becomes: /C:\Windows/ where the \W is erroneously interpreted as a non-word character class). The correct solution is to first escape any backslashes in regexp_part (the needed regex is actually: /C:\\Windows/).
To illustrate the correct way of handling this, here is a function which takes a passed phrase and creates a regex with the phrase wrapped in \b word boundaries:
// Given a phrase, create a RegExp object with word boundaries.
function makeRegExp(phrase) {
// First escape any backslashes in the phrase string.
// i.e. replace each backslash with two backslashes.
phrase = phrase.replace(/\\/g, "\\\\");
// Wrap the escaped phrase with \b word boundaries.
var re_str = "\\b"+ phrase +"\\b";
// Create a new regex object with "g" and "i" flags set.
var re = new RegExp(re_str, "gi");
return re;
}
// Here is a condensed version of same function.
function makeRegExpShort(phrase) {
return new RegExp("\\b"+ phrase.replace(/\\/g, "\\\\") +"\\b", "gi");
}
To understand this in more depth, follows is a discussion...
In-depth discussion, or "What's up with all these backslashes!?"
JavaScript has two ways to create a RegExp object:
/pattern/flags - You can specify a RegExp Literal expression directly, where the pattern is delimited using a pair of forward slashes followed by any combination of the three pattern modifier flags: i.e. 'g' global, 'i' ignore-case, or 'm' multi-line. This type of regex cannot be created dynamically.
new RegExp("pattern", "flags") - You can create a RegExp object by calling the RegExp() constructor function and pass the pattern as a string (without forward slash delimiters) as the first parameter and the optional pattern modifier flags (also as a string) as the second (optional) parameter. This type of regex can be created dynamically.
The following example demonstrates creating a simple RegExp object using both of these two methods. Lets say we wish to match the word "apple". The regex pattern we need is simply: apple. Additionally, we wish to set all three modifier flags.
Example 1: Simple pattern having no special characters: apple
// A RegExp literal to match "apple" with all three flags set:
var re1 = /apple/gim;
// Create the same object using RegExp() constructor:
var re2 = new RegExp("apple", "gim");
Simple enough. However, there are significant differences between these two methods with regard to the handling of escaped characters. The regex literal syntax is quite handy because you only need to escape forward slashes - all other characters are passed directly to the regex engine unaltered. However, when using the RegExp constructor method, you pass the pattern as a string, and there are two levels of escaping to be considered; first is the interpretation of the string and the second is the interpretation of the regex engine. Several examples will illustrate these differences.
First lets consider a pattern which contains a single literal forward slash. Let's say we wish to match the text sequence: "and/or" in a case-insensitive manner. The needed pattern is: and/or.
Example 2: Pattern having one forward slash: and/or
// A RegExp literal to match "and/or":
var re3 = /and\/or/i;
// Create the same object using RegExp() :
var re4 = new RegExp("and/or", "i");
Note that with the regex literal syntax, the forward slash must be escaped (preceded with a single backslash) because with a regex literal, the forward slash has special meaning (it is a special metacharacter which is used to delimit the pattern). On the other hand, with the RegExp constructor syntax (which uses a string to store the pattern), the forward slash does NOT have any special meaning and does NOT need to be escaped.
Next lets consider a pattern which includes a special: \b word boundary regex metasequence. Say we wish to create a regex to match the word "apple" as a whole word only (so that it won't match "pineapple"). The pattern (as seen by the regex engine) needs to be: \bapple\b:
Example 3: Pattern having \b word boundaries: \bapple\b
// A RegExp literal to match the whole word "apple":
var re5 = /\bapple\b/;
// Create the same object using RegExp() constructor:
var re6 = new RegExp("\\bapple\\b");
In this case the backslash must be escaped when using the RegExp constructor method, because the pattern is stored in a string, and to get a literal backslash into a string, it must be escaped with another backslash. However, with a regex literal, there is no need to escape the backslash. (Remember that with a regex literal, the only special metacharacter is the forward slash.)
Backslash SOUP!
Things get even more interesting when we need to match a literal backslash. Let's say we want to match the text sequence: "C:\Program Files\JGsoft\RegexBuddy3\RegexBuddy.exe". The pattern to be processed by the regex engine needs to be: C:\\Program Files\\JGsoft\\RegexBuddy3\\RegexBuddy\.exe. (Note that the regex pattern to match a single backslash is \\ i.e. each must be escaped.) Here is how you create the needed RegExp object using the two JavaScript syntaxes
Example 4: Pattern to match literal back slashes:
// A RegExp literal to match the ultimate Windows regex debugger app:
var re7 = /C:\\Program Files\\JGsoft\\RegexBuddy3\\RegexBuddy\.exe/;
// Create the same object using RegExp() constructor:
var re8 = new RegExp(
"C:\\\\Program Files\\\\JGsoft\\\\RegexBuddy3\\\\RegexBuddy\\.exe");
This is why the /regex literal/ syntax is generally preferred over the new RegExp("pattern", "flags") method - it completely avoids the backslash soup that can frequently arise. However, when you need to dynamically create a regex, as the OP needs to here, you are forced to use the new RegExp() syntax and deal with the backslash soup. (Its really not that bad once you get your head wrapped 'round it.)
RegexBuddy to the rescue!
RegexBuddy is a Windows app that can help with this backslash soup problem - it understands the regex syntaxes and escaping requirements of many languages and will automatically add and remove backslashes as required when pasting to and from the application. Inside the application you compose and debug the regex in native regex format. Once the regex works correctly, you export it using one of the many "copy as..." options to get the needed syntax. Very handy!
You should use the RegExp constructor to accomplish this:
var regexp2 = new RegExp(regexp_part + "weather");
Here's a related question that might help.
The forward slashes are just Javascript syntax to enclose regular expresions in. If you use normal string as regex, you shouldn't include them as they will be matched against. Therefore you should just build the regex like that:
var regexp2 = regexp_part + "weather";
I would use :
var regexp2 = new RegExp(regexp_part+"weather");
Like you have done that does :
var regexp2 = "/goodweather/";
And after there is :
test_string.match("/goodweather/")
Wich use match with a string and not with the regex like you wanted :
test_string.match(/goodweather/)
While this solution may be overkill for this specific question, if you want to build RegExps programmatically, compose-regexp can come in handy.
This specific problem would be solved by using
import {sequence} from 'compose-regexp'
const weatherify = x => sequence(x, /weather/)
Strings are escaped, so
weatherify('.')
returns
/\.weather/
But it can also accept RegExps
weatherify(/./u)
returns
/.weather/u
compose-regexp supports the whole range of RegExps features, and let one build RegExps from sub-parts, which helps with code reuse and testability.
Do i have to escape slashes when putting them into regular expression?
myString = '/courses/test/user';
myString.replace(/\/courses\/([^\/]*)\/.*/, "$1");
document.write(myString);
Instead of printing "test", it prints the whole source string.
See this demo:
http://jsbin.com/esaro3/2/edit
Your regex is perfect, and yes, you must escape slashes since JavaScript uses the slashes to indicate regexes.
However, the problem is that JavaScript's replace method does not perform an in-place replace. That is, it does not actually change the string -- it just gives you the result of the replace.
Try this:
myString = '/courses/test/user';
myString = myString.replace(/\/courses\/([^\/]*)\/.*/, "$1");
document.write(myString);
This sets myString to the replaced value.
/[\/]/g matches forward slashes.
/[\\]/g matches backward slashes.
Actually, you don't need to escape the slash when inside a character class as in one part of your example (i.e., [^\/]* is fine as just [^/]*). If it is outside of a character class (like with the rest of your example such as \/courses), then you do need to escape slashes.
string.replace doesn't modify the original string. Instead, a returns a new string that has had the replacement performed.
Try:
myString = '/courses/test/user';
document.write(myString.replace(/\/courses\/([^\/]*)\/.*/, "$1"));
Note, that you don't have to escape / if you use new RegExp() constructor:
console.log(new RegExp("a/b").test("a/b"))
I am trying use javascript regular expressions to do some matching and I found a really unusual behavior that I was hoping someone could explain.
The string I was trying to match was: " 0 (IR) " and the code block was
finalRegEx = new RegExp("[0-9]");
match = finalRegEx.exec(str);
except that when I put "\d" instead of "[0-9]" it didn't find a match. I'm really confused by this.
If you use RegExp with "\d" to build the regular expression, the "\d" will result in just "d". Either use two back slashes to escape the slash like "\\d" or simply use the regular expression literals /…/ instead:
match = /\d/.exec(str)
You need to escape it because you're using the constructor, otherwise it matches d literally:
new RegExp('\\d').test('1')
new RegExp should only be used for dynamic matching. Otherwise use a literal:
var foo = /\d/;
foo.test(1)
You probably need to escape the backslash: finalRegEx = new RegExp("\\d");