CODEWITHSUNDEEP
javascriptregex
bittersweetryan
bittersweetryan

Reputation: 3453

Why doesn't this RegEx work in JavaScript?

I'm trying to match the text "foo" between the two brackets in this following statement:

Expected [foo] but Recieved [__]

I'm then trying to replace the text with "...". When I run the following code I get an invalid grouping error in JavaScript. When I run the expression in Regexr it works the way I expect it to. 

var text = $("#assertion").html().replace( /(?<=Expected \[).*(?=\] )/,"...");

http://jsfiddle.net/bittersweetryan/VcraW/

Upvotes: 1

Views: 593

Answers (2)

hugomg
hugomg

Reputation: 69984

Javascript regexes don't understand lookbacks (the ?<=). You need to match the Expected [ part explicitely:

replace(/(Expected \[)[^\]]*/, "$1...")

The $1 is to avoid retyping the "Expected [" part and I changed the rest of the regex a bit to avoid greedy matching with .*

http://jsfiddle.net/VcraW/2/

Upvotes: 6

stema
stema

Reputation: 93086

Because javascript does not support look behind assertions.

You can work around by putting this in a capturing group and using this in the replacement

.replace( /(Expected \[).*(?=\] )/,"$1...");

The content of the first pair of brackets is stored in the capturing group 1 and you can get this back using $1

Upvotes: 3

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