Regex inside `if` check

Question

I'm trying to use regex inside if. Strange, but it doesn't work. How it may be fixed?

It works:

var lang = 'lang-js'; if (lang == 'lang-js') { alert('ok'); }

It works too (just for testing purposes):

var lang = 'lang-js'; if (lang == 'lang-' + 'js') { alert('ok'); }

But this one doesn't work:

var lang = 'lang-js'; if (lang == 'lang-' + /[a-z]/) { alert('not ok'); }

Type 'lang-' + /[a-z]/ in the browser console and see what happens. You're not doing a regular expression test, you are concatenating a regex with a string, which produces a string, and then comparing that with another string. This has nothing to do with jQuery so I've removed that tag. — nnnnnn
– nnnnnn, Commented Mar 1, 2017 at 1:54

Daniel A. White · Accepted Answer · 2017-03-01 01:55:32Z

5

use something like this

if (/^lang-[a-z]/.test(lang)) {

you might have to adjust the regex as this just looks for one char.

answered Mar 1, 2017 at 1:55

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Comments

MypKOT-1992 · Accepted Answer · 2017-03-01 02:06:12Z

its because typeof /[a-z]/ == 'object' and where ''+/[a-z]/ working toString and your result will be string lang-/[a-z]/