javascript regex for matching all strings that isn't a specified string

Question

I have a regex that looks like the following:

var myRegex = /%([a-z_]*)%/i

This matches any substring such as %foo% where a string is between two quotes.

What's the best way to modify this regex so that it only matches when the regex matches when % surrounds anything BUT the string foo? So it won't match %foo% but it would match %bar_% %anythingelse%?

anubhava · Accepted Answer · 2016-11-28 19:59:51Z

3

You're looking for a negative lookahead here:

var myRegex = /%(?!foo%)([a-z_]*)%/i;

(?!foo%) is negative lookahead that will assert failure when we have foo% is ahead of % thus failing %foo%.

answered Nov 28, 2016 at 19:59

anubhava

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5 Comments

Jay Over a year ago

Wouldn't this incorrectly not match %foolkajsdksad%?

Jecoms Over a year ago

@Jay No, because foo% is a string literal. There are no wildcards between foo and %

Gavin Over a year ago

@Jay Nope, because the negative lookahead looks for foo% instead of foo

Jay Over a year ago

what about %alskjdfoo%?

Jay Over a year ago

So I tested it out, but I'm not really sure why it should match that string haha

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