javascript regexp does not allow my expression

Question

I'm wanting to use javascript regexp to test if my string matches a regular expression. However, the regular expression that I'm trying to use causes my javascript to break.

I understand that I can typically do the following:

/e/.test("blah")

but when I try to use my expression, my browser barfs:

/(?<=^| )\d+(\.\d+)?(?=$| )|(?<=^| )\.\d+(?=$| )/.test("1.23")

What am I missing?

Javascript does not support look-behind assertions.

hwnd
– hwnd

2014-10-02 22:46:46 +00:00
Commented Oct 2, 2014 at 22:46 — hwnd
– hwnd, Commented Oct 2, 2014 at 22:46
Why is this tagged R?

Rich Scriven
– Rich Scriven

2014-10-02 22:47:28 +00:00
Commented Oct 2, 2014 at 22:47 — Rich Scriven
– Rich Scriven, Commented Oct 2, 2014 at 22:47

hwnd · Accepted Answer · 2014-10-02 23:06:03Z

2

Javascript does not support Negative or Positive Lookbehind assertions. Therefore, your browser should be throwing an error for Invalid regular expression: ( Invalid group ) because of the Positive Lookbehind (?<=^| ) ...

I would start off with using beginning of string ^ and end of string $ anchors ..

/^\d+(?:\.\d+)?$/.test("1.23")

And if you really want to assert the beginning of string/whitespace or end of string/whitespace positions, you could compile them using capturing groups instead of lookaround assertions since you are only using the test method.

/(^| ) PATTERN ($| )/

edited Oct 2, 2014 at 23:06

answered Oct 2, 2014 at 22:50

hwnd

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