Trouble defining a proper RegEx in Javascript

Question

I need to create a regular expression that matches a process number that has the following pattern #######-##.####.7.09.0009 where # means numbers from 0 to 9. Here is what I came up with after some research:

var regex = new RegExp("^[0-9]{7}[\-][0-9]{2}[\.][0-9]{4}[\.7\.09\.0009]$");

I also tried:

/^[0-9]{7}\-[0-9]{2}\.[0-9]{4}\.7\.09\.0009$/
/^[0-9]{7}\\-[0-9]{2}\\.[0-9]{4}\\.7\\.09\\.0009$/

You don't have to put [\.7\.09\.0009] in square brackets or else it would mean a character class. — The fourth bird
– The fourth bird, Commented Sep 27, 2018 at 18:21
You have to double-escape backslashes when using new RegExp(String) — Luca Kiebel
– Luca Kiebel, Commented Sep 27, 2018 at 18:22
Your second pattern works using anchors to assert the start and the end of the line. — The fourth bird
– The fourth bird, Commented Sep 27, 2018 at 18:39

Donut · Accepted Answer · 2018-09-27 18:21:15Z

4

Try this:

const pattern = /\d{7}\-\d{2}\.\d{4}\.7\.09\.0009/

Regexper is a great tool that I use whenever I'm writing a regular expression, I find it really helps to visualize what the expression is actually doing. Check it out.

For reference, here is the original pattern that you posted -- it looks like the main problem is that you are defining character classes in several places using [ and ] where you really don't need them at all.

answered Sep 27, 2018 at 18:21

Donut

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2 Comments

Alexandre Krabbe Over a year ago

So I should do const pattern = /\d{7}\-\d{2}\.\d{4}\.7\.09\.0009/ and then regex = new RegExp(pattern) ? Maybe the problem lies somewhere else then because alert(/\d{7}\-\d{2}\.\d{4}\.7\.09\.0009/.test($('#numero-processo').val())); returns false. Here is what alert($('#numero-processo').val()); returns 1111111-11.1111.7.09.009 Shouldn't it be working?

Donut Over a year ago

Nah, pattern is a regex literal (developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/…) so you don't need new RegExp(pattern), you can just do pattern.test. What you posted is expected behavior though - "1111111-11.1111.7.09.009" does not match the regex (it should end with "0009", like this: "1111111-11.1111.7.09.0009")

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