Using search and replace with regex in javascript

Question

I have a regular expression that I have been using in notepad++ for search&replace to manipulate some text, and I want to incorporate it into my javascript code. This is the regular expression:

Search (?-s)(.{150,250}\.(\[\d+\])*)\h+ and replace with \1\r\n\x20\x20\x20

In essence creating new paragraphs for every 150-250 words and indenting them.

This is what I have tried in JavaScript. For a text area <textarea name="textarea1" id="textarea1"></textarea>in the HTML. I have the following JavaScript:

function rep1() {
    var re1 = new RegExp('(?-s)(.{150,250}\.(\[\d+\])*)\h+');
    var re2 = new RegExp('\1\r\n\x20\x20\x20');
    var s = document.getElementById("textarea1").value;
    s = string.replace(re1, re2);
    document.getElementById("textarea1").value = s;
}

I have also tried placing the regular expressions directly as arguments for string.replace() but that doesn't work either. Any ideas what I'm doing wrong?

(?-s) is not valid in JS engine test here

Code Maniac
– Code Maniac

2019-03-16 14:43:06 +00:00
Commented Mar 16, 2019 at 14:43 — Code Maniac
– Code Maniac, Commented Mar 16, 2019 at 14:43
Where is your function executed?

Quentin
– Quentin

2019-03-16 14:43:53 +00:00
Commented Mar 16, 2019 at 14:43 — Quentin
– Quentin, Commented Mar 16, 2019 at 14:43

trincot · Accepted Answer · 2019-03-16 21:05:15Z

2

Several issues:

JavaScript does not support (?-s). You would need to add modifiers separately. However, this is the default setting in JavaScript, so you can just leave it out. If it was your intention to let . also match line breaks, then use [^] instead of . in JavaScript regexes.
JavaScript does not support \h -- the horizontal white space. Instead you could use [^\S\r\n].
When passing a string literal to new RegExp be aware that backslashes are escape characters for the string literal notation, so they will not end up in the regex. So either double them, or else use JavaScript's regex literal notation
In JavaScript replace will only replace the first occurrence unless you provided the g modifier to the regular expression.
The replacement (second argument to replace) should not be a regex. It should be a string, so don't apply new RegExp to it.
The backreferences in the replacement string should be of the $1 format. JavaScript does not support \1 there.
You reference string where you really want to reference s.

This should work:

function rep1() {
    var re1 = /(.{150,250}\.(\[\d+\])*)[^\S\r\n]+/g;
    var re2 = '$1\r\n\x20\x20\x20';
    var s = document.getElementById("textarea1").value;
    s = s.replace(re1, re2);
    document.getElementById("textarea1").value = s;
}

edited Mar 16, 2019 at 21:05

answered Mar 16, 2019 at 14:57

trincot

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2 Comments

Floran Thovan Over a year ago

Fantastic answer, it would have taken me ages to write it myself, so thank you so much for taking the time to do it, much appreciated !

trincot Over a year ago

Ah, you're right, @WiktorStribiżew. Updated accordingly!

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