Alternative javascript alternative

Question

I tried using lookahead / lookbehind in JavaScript (described in Regular-Expressions.info ) and realized that they were not supported.

What I'm trying to do is catch dar, which should not be followed win. So, the string darblablashould return true, but it darwinblablashould be false.

Now my decision: /dar/i.test(string) && !/darwin/i.test(string).

It looks pretty long, is there a shorter solution (regex string?) That can replace the current statement?

Answer 1

Here is the solution

^dar(?!win)

Demo version of Debuggex

EDIT

Regarding your second question

^(?!cyg)win

Demo version of Debuggex

Answer 2

Javascript .

alert(/dar(?!win)/.test('darblahblah'))
alert(/dar(?!win)/.test('darwin'))

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Answer 3

You cannot use look-backs in JavaScript, but you can use advances.

So this will give false:

document.write(/\bdar(?!win)/i.test("darwin"));

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As for the look, in most cases you can get around this limitation by using capture groups, return lines and matches, or by creating your own parsers.

Here is a way to combine /win/i.test(string) && !/cyg win/i.test(string):

document.write(/niw(?!\s+gyc\b)/.test('cyg win'.split("").reverse().join("")));
document.write("<br/>");
document.write(/niw(?!\s+gyc\b)/.test('darwin'.split("").reverse().join("")));

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Note that the - niw(?!\s+gyc\b)- pattern must be canceled.