Dynamic regex pattern in JavaScript

Question

I have some code that matches a certain number of digits after a decimal. Currently, I have the following:

var input = getValueFromUser();
var count = getCount();
var x = Number(input.toString().match(/^\d+(?:\.\d{0,1})?/));
alert(x);

This approach always gets the first digit after the decimal. However, I want to replace the 1 in the regex with the value in count. How do I do that? I tried the following:

var pattern = '/^\d+(?:\.\d{0,' + count + '})?/';
var x = Number(input.toString().match(pattern));

However, now, I always get 0 for x.

You have to use Regexp object if you want to use dynamic patterns — hindmost
– hindmost, Commented Nov 6, 2014 at 13:48

Bakudan · Accepted Answer · 2019-09-25 08:47:11Z

6

You have to use Regexp object if you want to use dynamically built patterns:

var re = new RegExp('^\\d+(?:\\.\\d{0,' + count + '})?');

edited Sep 25, 2019 at 8:47

Bakudan

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answered Nov 6, 2014 at 13:50

hindmost

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1 Comment

nnnnnn Over a year ago

Note that the backslashes in the string need to be escaped (unlike backslashes in a regex literal).

Asis Datta · Accepted Answer · 2014-11-06 14:07:23Z

0

This will help you.

var pattern = '^\\d+(?:\\.\\d{0,' + '5' + '})?',
    reg=new RegExp(pattern),
    x = Number(input.toString().match(reg));

edited Nov 6, 2014 at 14:07

answered Nov 6, 2014 at 13:52

Asis Datta

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1 Comment

nnnnnn Over a year ago

Don't include the / at the beginning and end of the regex pattern if supplying it as a string - that's for regex literals only. Also if the pattern is in a string you need to escape the backslashes.

Mohamad reza1987 · Accepted Answer · 2020-09-12 12:40:11Z

0

mask: new RegExp(`^[a-zA-Z0-9]{0,${maxLength}}$`)

its work for me

answered Sep 12, 2020 at 12:40

Mohamad reza1987

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Comments

Ajay Takur · Accepted Answer · 2022-07-09 13:39:31Z

0

var alien = 'ajay'+' $%';
var all=new RegExp(`${alien}`)

answered Jul 9, 2022 at 13:39

Ajay Takur

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