adding dynamic values to regex

Question

I am having a regex where i check the input is having 6 digit number. I am able to achieve it with the below refgex

/^\d{6}$/gm.test("123456")

I have used this regex in multiple places so I am trying to make it as a function

function testNumber(number, digitLength = 6){
  return /^\d{6}$/gm.test(number)
}

Now in some places the digitLength is of 3 and in some places its 4, now how can i interpolate the digitLength in the regex so i can pass as much the digitLength instead of hardcoding 6 in the regex.

Any help is appreciated

@CherryDT yep template literals would be easy but where to add so that why I am confused, without failing the regex — dev
– dev, Commented Dec 10, 2021 at 9:05
so there is no way to interpolate variables inside regex string ? — dev
– dev, Commented Dec 10, 2021 at 9:06
See also: Use dynamic (variable) string as regex pattern in JavaScript — CherryDT
– CherryDT, Commented Dec 10, 2021 at 9:08

Thomas · Accepted Answer · 2021-12-10 09:32:34Z

2

Instead of a dynamic regex you could also do it like this:

function testNumber(number, digitLength = 6){
  return number.length === digitLength // check expected length
    && /^\d+$/.test(number);           // and that it is all digits
}

answered Dec 10, 2021 at 9:32

Thomas

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Xeelley · Accepted Answer · 2021-12-10 09:45:10Z

2

You are looking for (your regex):

function testNumber(number, digitLength = 6){
  return new RegExp(`^\\d{${digitLength}}$`, 'gm').test(number);
}

Refs: RegExp, Template literals.

Same, but optimized:
As @Thomas noticed, you don't need g flag in your case, because you always match global (full string), and you don't need m flag too, because you accept one-line inputs. So regex like this is enough:

function testNumber(number, digitLength = 6){
  return new RegExp(`^\\d{${digitLength}}$`).test(number);
}

edited Dec 10, 2021 at 9:45

answered Dec 10, 2021 at 9:07

Xeelley

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2 Comments

Thomas Over a year ago

Why gm? There's no need for global nor multiline here. We always match the entire string.

Xeelley Over a year ago

@Thomas make sence, I'll update answer, thanks for advice!

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