javascript regex, word not followed and not preceded by specific char

Question

I guess I'm not very good at regular expressions, so here is my problem (I'm sure it's easy to solve, but somehow I can't seem to find how )

var word = "aaa";
text = text.replace( new RegExp(word, "g"),
                     "<span style='background-color: yellow'>"+word+"</span>");

this is working in most cases.

What I want to do is for the regex ONLY TO WORK when word is not followed by the char / and not preceded with char ".

score 14 · Accepted Answer · edited Nov 13 '18 at 22:33

14

You're going to want to use a negative look-ahead.

Regex: '[^"]' + word + '(?!/)'

Edit: While it doesn't matter as it appears you already found your answer by avoiding look-behinds, Rohit noticed something I didn't. You're going to need to capture the [^\"] and include it in the replace so that it does not get discarded. This wasn't necessary for the look-head since look-arounds by definition aren't included in captures.

edited Nov 13 '18 at 22:33

Daniel Foust

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answered Dec 24 '12 at 08:43

Michael

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thanks alot. so if i also want it to not to be preceded by char " i should make it "(?!\")" + word + "(?!\/)" ? – MirrorMirror Dec 24 '12 at 08:46
If you want to make sure " does not precede word, you need to use a negative look-behind. So you would need `(? – Michael Dec 24 '12 at 08:48
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Javascript does not supprt look-behinds. – Rohit Jain Dec 24 '12 at 08:51
new RegExp("(? – MirrorMirror Dec 24 '12 at 08:52
@RohitJain Ah well then since negative look-behinds don't work, you can just use a negated character class. `[^\"] + word + (?!\/)`. Thanks for the heads up. – Michael Dec 24 '12 at 08:54
indeed it can't look behind. i solved it by checking two characters, as it should not find it if it also has a number after the slash, so no need to look behind. solution: word+"(?!\/[0-9])", "gi". the preceding [^\"] that you posted breaks things. – MirrorMirror Dec 24 '12 at 09:01
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`'[^"]' + word + '(?!/)'` is enough. – nhahtdh Dec 24 '12 at 09:03

Rohit Jain · Answer 2 · 2012-12-24T09:09:55.740

3

You can use this regex: -

'([^"])' + word + '(?!/)'

and replace it with - "$1g"

Note that Javascript does not support look-behinds. So, you need to capture the previous character and ensure that it is not ", using negated character class.

See demo at http://fiddle.re/zdjt

edited Dec 24 '12 at 09:09

answered Dec 24 '12 at 08:53

Rohit Jain

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This fails if the match is at beginning or end of line. Perhaps the question could mention whether this matters. – tripleee Dec 24 '12 at 09:02

javascript regex, word not followed and not preceded by specific char

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