Javascript Regex not working on script but working on console

Question

I'm trying to validate only 4 numbers like this:

It is working on the above page, but when I use it on a script it is not working:

var reg = new RegExp('^\d{4}$/');
reg.test(1234);
reg.test('1234');

Both are returning false...

If I test on the browser console like this:

/^\d{4}$/.test('1234');
/^\d{4}$/.test(1234);

Both are returning true.

What I'm missing?

You could simply use /^\d{4}$/.test(1234) directly in your code ? — Nicolas
– Nicolas, Commented Nov 8, 2017 at 16:14
And if you still need the variable you should initialize it like this var reg = RegExp(/^\d{4}$/) — Lixus
– Lixus, Commented Nov 8, 2017 at 16:14
looks like you're missing a single slash '^\d{4}$/' should be '/^\d{4}$/' — Robbie Milejczak
– Robbie Milejczak, Commented Nov 8, 2017 at 16:15
You're using different code in your script vs. the console. That's why you're getting different results. — JLRishe
– JLRishe, Commented Nov 8, 2017 at 16:17
@RobbieMilejczak - close . . . you don't use the opening and closing slashes in a string parameter for the RegExp constructor. Also the \d needs to have its slash escaped in a RegExp string parameter (i.e., \\d). Basically, Chin Leung nailed it in his answer below. :) — talemyn
– talemyn, Commented Nov 8, 2017 at 16:19

Chin Leung · Accepted Answer · 2017-11-08 16:16:29Z

13

The problem is because your RegExp is not initialized properly.

You can either do:

// Note the \\ to escape the backslash
var reg = new RegExp('^\\d{4}$');

Or

var reg = new RegExp(/^\d{4}$/);

answered Nov 8, 2017 at 16:16

Chin Leung

15k4 gold badges38 silver badges64 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

this helped me, can't reuse it each time apparently