Error using both lookahead and look behind regex

Question

I am having a problem using the following regex. It works fine in regexr and rubular but it gives me an error when running it on node.js. I am fairly new to using regex and i'm not sure what i'm doing wrong. It will work if I knock off the (?<= ) so I presume that is the problem.

I'm trying to match 'is' with a leading and trailing space using /(?<= )is(?= )|==/g

Example with test words:
http://regexr.com?33781

Node error output

 temp = temp.replace(/(?<= )is(?= )|==/g, '===');
^
SyntaxError: Invalid regular expression: /(?<= )is(?= )|==/: Invalid group
at new RegExp (unknown source)

score 15 · Accepted Answer · answered Dec 21 '12 at 16:34

JavaScript regex does not support lookbehind at all.

Sources:

However, you can fake it in some cases.

score 2 · Answer 2 · answered Dec 21 '12 at 16:34

2

Quite simply, this is because JavaScript regular expressions have no support for lookbehinds:

http://www.regular-expressions.info/javascript.html

Lookbehind is not supported at all. Lookahead is fully supported.

answered Dec 21 '12 at 16:34

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Error using both lookahead and look behind regex

2 Answers2

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