How does JavaScript detect regular expressions?

Question

I am writing a JS parser, and am wondering how to differentiate between a regular expression (/lookup/g) and simple division (bar/baz/g). What are the rules that JavaScript uses to identify regular expressions?

alex · Accepted Answer · 2012-04-15 13:39:15Z

11

You want to check out Section 7.8.5 in the ECMA spec (the annotated version is up-to-date currently, but always check the latest PDF from the ECMA).

Remember too that a JavaScript regex can not be empty. // is always the start of a single line comment. It's also worth mentioning that a semicolon must never be inserted before a regex literal.

Tangential, an empty JavaScript regex looks like /(?:)/.

Further discussion.

edited Apr 15, 2012 at 13:39

answered Nov 30, 2011 at 22:54

alex

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4 Comments

Andrew Marshall Over a year ago

Note that the grammar appears to have changed a bit in the latest version.

alex Over a year ago

@AndrewMarshall: I would of linked that if it were in HTML format - do you know if one exists? Thanks.

Andrew Marshall Over a year ago

Yea that's why I figured you'd linked to that version instead. And no I don't, unfortunately. I just wanted to add the link to the latest version for completeness sake.

kubetz Over a year ago

@alex: Here is the link again. I deleted the comment by accident (don't ask).

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