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How to make replace() global in JavaScript

I know this question had been asked lot of time but i could not find solution. I have some smilies which each of them has code to be rendered as smiley using replace() , but I get syntax error, I don't know why and how to render my code :/ to smiley
txt = " Hi :/ ";
txt.replace("/\:/\/g","<img src='img/smiley.gif'>");

Your regular expression doesn't need to be in quotes. You should escape the correct / forward slash (you were escaping the wrong slash) and assign the replacement, since .replace doesn't modify the original string.
txt = " Hi :/ ";
txt = txt.replace(/:\//g,"<img src='img/smiley.gif'>");
Based on jonatjano's brilliant deduction, I think you should add a little more to the regular expression to avoid such calamities as interfering with URLs.
txt = txt.replace(/:\/(?!/)/g,"<img src='img/smiley.gif'>");
The above ensures that :// is not matched by doing a negative-lookahead.

There are two problems in the first argument of replace() it escapes the wrong characters and it uses a string that seems to contain a regex instead of a real RegExp.
The second line should read:
txt.replace(/:\//g,"<img src='img/smiley.gif'>");
/:\//g is the regex. The first and the last / are the RegExp delimiters, g is the "global" RegExp option (String.replace() needs a RegExp instead of a string to do a global replace).
The content of the regex is :/ (the string you want to find) but because / has a special meaning in a RegExp (see above), it needs to be escaped and it becomes :\/.

javascript regex replace multiline strings [duplicate]

var ss= "<pre>aaaa\nbbb\nccc</pre>ddd";
var arr= ss.match( /<pre.*?<\/pre>/gm );
alert(arr); // null
I'd want the PRE block be picked up, even though it spans over newline characters. I thought the 'm' flag does it. Does not.
Found the answer here before posting. SInce I thought I knew JavaScript (read three books, worked hours) and there wasn't an existing solution at SO, I'll dare to post anyways. throw stones here
So the solution is:
var ss= "<pre>aaaa\nbbb\nccc</pre>ddd";
var arr= ss.match( /<pre[\s\S]*?<\/pre>/gm );
alert(arr); // <pre>...</pre> :)
Does anyone have a less cryptic way?
Edit: this is a duplicate but since it's harder to find than mine, I don't remove.
It proposes [^] as a "multiline dot". What I still don't understand is why [.\n] does not work. Guess this is one of the sad parts of JavaScript..

DON'T use (.|[\r\n]) instead of . for multiline matching.
DO use [\s\S] instead of . for multiline matching
Also, avoid greediness where not needed by using *? or +? quantifier instead of * or +. This can have a huge performance impact.
See the benchmark I have made: https://jsben.ch/R4Hxu
Using [^]: fastest
Using [\s\S]: 0.83% slower
Using (.|\r|\n): 96% slower
Using (.|[\r\n]): 96% slower
NB: You can also use [^] but it is deprecated in the below comment.

[.\n] does not work because . has no special meaning inside of [], it just means a literal .. (.|\n) would be a way to specify "any character, including a newline". If you want to match all newlines, you would need to add \r as well to include Windows and classic Mac OS style line endings: (.|[\r\n]).
That turns out to be somewhat cumbersome, as well as slow, (see KrisWebDev's answer for details), so a better approach would be to match all whitespace characters and all non-whitespace characters, with [\s\S], which will match everything, and is faster and simpler.
In general, you shouldn't try to use a regexp to match the actual HTML tags. See, for instance, these questions for more information on why.
Instead, try actually searching the DOM for the tag you need (using jQuery makes this easier, but you can always do document.getElementsByTagName("pre") with the standard DOM), and then search the text content of those results with a regexp if you need to match against the contents.

You do not specify your environment and version of JavaScript (ECMAScript), and I realise this post was from 2009, but just for completeness:
With the release of ECMA2018 we can now use the s flag to cause . to match \n (see https://stackoverflow.com/a/36006948/141801).
Thus:
let s = 'I am a string\nover several\nlines.';
console.log('String: "' + s + '".');
let r = /string.*several.*lines/s; // Note 's' modifier
console.log('Match? ' + r.test(s)); // 'test' returns true
This is a recent addition and will not work in many current environments, for example Node v8.7.0 does not seem to recognise it, but it works in Chromium, and I'm using it in a Typescript test I'm writing and presumably it will become more mainstream as time goes by.

Now there's the s (single line) modifier, that lets the dot matches new lines as well :)
\s will also match new lines :D
Just add the s behind the slash
/<pre>.*?<\/pre>/gms

[.\n] doesn't work, because dot in [] (by regex definition; not javascript only) means the dot-character. You can use (.|\n) (or (.|[\n\r])) instead.

I have tested it (Chrome) and it's working for me (both [^] and [^\0]), by changing the dot (.) with either [^\0] or [^] , because dot doesn't match line break (See here: http://www.regular-expressions.info/dot.html).
var ss= "<pre>aaaa\nbbb\nccc</pre>ddd";
var arr= ss.match( /<pre[^\0]*?<\/pre>/gm );
alert(arr); //Working

In addition to above-said examples, it is an alternate.
^[\\w\\s]*$
Where \w is for words and \s is for white spaces

[\\w\\s]*
This one was beyond helpful for me, especially for matching multiple things that include new lines, every single other answer ended up just grouping all of the matches together.

Greedy Regex for varying number of new line [duplicate]

var ss= "<pre>aaaa\nbbb\nccc</pre>ddd";
var arr= ss.match( /<pre.*?<\/pre>/gm );
alert(arr); // null
I'd want the PRE block be picked up, even though it spans over newline characters. I thought the 'm' flag does it. Does not.
Found the answer here before posting. SInce I thought I knew JavaScript (read three books, worked hours) and there wasn't an existing solution at SO, I'll dare to post anyways. throw stones here
So the solution is:
var ss= "<pre>aaaa\nbbb\nccc</pre>ddd";
var arr= ss.match( /<pre[\s\S]*?<\/pre>/gm );
alert(arr); // <pre>...</pre> :)
Does anyone have a less cryptic way?
Edit: this is a duplicate but since it's harder to find than mine, I don't remove.
It proposes [^] as a "multiline dot". What I still don't understand is why [.\n] does not work. Guess this is one of the sad parts of JavaScript..

DON'T use (.|[\r\n]) instead of . for multiline matching.
DO use [\s\S] instead of . for multiline matching
Also, avoid greediness where not needed by using *? or +? quantifier instead of * or +. This can have a huge performance impact.
See the benchmark I have made: https://jsben.ch/R4Hxu
Using [^]: fastest
Using [\s\S]: 0.83% slower
Using (.|\r|\n): 96% slower
Using (.|[\r\n]): 96% slower
NB: You can also use [^] but it is deprecated in the below comment.

[.\n] does not work because . has no special meaning inside of [], it just means a literal .. (.|\n) would be a way to specify "any character, including a newline". If you want to match all newlines, you would need to add \r as well to include Windows and classic Mac OS style line endings: (.|[\r\n]).
That turns out to be somewhat cumbersome, as well as slow, (see KrisWebDev's answer for details), so a better approach would be to match all whitespace characters and all non-whitespace characters, with [\s\S], which will match everything, and is faster and simpler.
In general, you shouldn't try to use a regexp to match the actual HTML tags. See, for instance, these questions for more information on why.
Instead, try actually searching the DOM for the tag you need (using jQuery makes this easier, but you can always do document.getElementsByTagName("pre") with the standard DOM), and then search the text content of those results with a regexp if you need to match against the contents.

You do not specify your environment and version of JavaScript (ECMAScript), and I realise this post was from 2009, but just for completeness:
With the release of ECMA2018 we can now use the s flag to cause . to match \n (see https://stackoverflow.com/a/36006948/141801).
Thus:
let s = 'I am a string\nover several\nlines.';
console.log('String: "' + s + '".');
let r = /string.*several.*lines/s; // Note 's' modifier
console.log('Match? ' + r.test(s)); // 'test' returns true
This is a recent addition and will not work in many current environments, for example Node v8.7.0 does not seem to recognise it, but it works in Chromium, and I'm using it in a Typescript test I'm writing and presumably it will become more mainstream as time goes by.

Now there's the s (single line) modifier, that lets the dot matches new lines as well :)
\s will also match new lines :D
Just add the s behind the slash
/<pre>.*?<\/pre>/gms

[.\n] doesn't work, because dot in [] (by regex definition; not javascript only) means the dot-character. You can use (.|\n) (or (.|[\n\r])) instead.

I have tested it (Chrome) and it's working for me (both [^] and [^\0]), by changing the dot (.) with either [^\0] or [^] , because dot doesn't match line break (See here: http://www.regular-expressions.info/dot.html).
var ss= "<pre>aaaa\nbbb\nccc</pre>ddd";
var arr= ss.match( /<pre[^\0]*?<\/pre>/gm );
alert(arr); //Working

In addition to above-said examples, it is an alternate.
^[\\w\\s]*$
Where \w is for words and \s is for white spaces

[\\w\\s]*
This one was beyond helpful for me, especially for matching multiple things that include new lines, every single other answer ended up just grouping all of the matches together.

Javascript RegEx to find first line of each paragraph

This is probably a simple one but I'm very much a regex novice.
I'm looking to select the first line of every paragraph within a textarea on a page using a regular expression. After thinking I was there I have hit a problem.
Using http://gskinner.com/RegExr/ I came up with this:
/\r\r.*\r/g
but then I place that into my javascript and ran it on the page:
var headingsArr = document.getElementById("text").value.match(/\r\r.*\r/g);
and the array returns null.
Have I got the regular expression right and if so where am I going wrong when using it in my javascript!?
Thank you

This depends on what your newline characters are. I think you may better go for
/(?:\r\n|[\r\n]){2}.*(?:\r\n|[\r\n])/g
I know in Regexr only a \r is a newline. But in Windows normally \r\n is used, but under .*ix its normally only the \n.
So (?:\r\n|[\r\n]) is an alternation, it tries at first to match \r\n if this is not found it matches either \r or \n.

For the sake of future searchers, if you just need to style the first line of text, you can use the css pseudoclass ::first-line :
textarea::first-line {
background-color: yellow;
}
http://www.w3schools.com/cssref/sel_firstline.asp

Javascript regex validate password string (escaping punctuations)

I am trying to validate a password string with javascript and need some help with a regex. I have tried some tutorials, but I think I have some problems understanding how to escape quantifiers and/or metacharacters.
I want to make sure that the password string only contains one or more (max 32) characters from the following spans:
"abcdefghijklmnopqrstuvwxyz"
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"012345678901234567890123456789"
"!##%&/(){}[]=?+*^~-_.:,;"
The first three spans are pretty easy, but I can't figure out the last one. Basically my script looks something like this:
var password = "user_input_password";
if (/^[A-Za-z0-9!##$%...]{1,32}$/.test(password)) {
document.write('OK');
} else {
document.write('Not OK');
}
Any help or input is highly appreciated, thanks!

In general, you can escape a meta-character using a backslash \; however, inside a character class, the only ones you have to escape are ] , \ and - (the ^ only has a meaning at the very beginning). Something like [\w!##%&/(){}[\]=?+*^~\-.:,;] will do what you want.
The \w is equal to [A-Za-z0-9_].
So the full test would be something like:
/^[\w!##%&/(){}[\]=?+*^~\-.:,;]{1,32}$/.test(password)

/^[A-Za-z0-9!##%&\/(){}\[\]=?+*^~\-_\.:,;]{1,32}$/

You can also match all characters that are not considered white space (space, newline, tab)
/^[^\s]{1,32}$/.test(password);
To exclude quotes as well (I didn't see them in your example) you can add those in:
/^[^\s'"]{1,32}$/.test(password);