JS RegEx to match certain patterns only

Question

I need to adapt my Javascript RegEx to match certain patterns only. The RegEx is used in the html5 pattern attribute to validate an input field.

I want to accept alphanumeric pattern of the following types only:

A-AAAA or BB-BBB (the intended pattern is: 1 digit before the "-", and 4 digits after the "-", or 2 digits before the "-", and 3 digits after the "-").

My current RegEx is:

/([\w]{1,2})(-([\w]{3,4}))/g

This one works, but accepts CC-CCCC as well, which is obviously a valid input pattern, but not the intended pattern. It accepts DDD-DDDD as well; valid again, but not intended.

Could you please assist adapting the pattern?

Use start and end anchors, and have your 2 patterns separated by |. regex101.com/r/uV8gI4/1#javascript — user1106925
– user1106925, Commented Sep 4, 2016 at 15:00

anubhava · Accepted Answer · 2016-09-05 07:14:02Z

2

You can use alternation based regex in HTML5 pattern attribute (as it has implicit anchors):

/(?:\w-\w{4}|\w{2}-\w{3})/

RegEx Demo

edited Sep 5, 2016 at 7:14

answered Sep 4, 2016 at 15:00

anubhava

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5 Comments

Otto Over a year ago

Thank you very much. This one well solved my problem!

anubhava Over a year ago

@torazaburo: \b is used for word boundary in this regex.

user663031 Over a year ago

My question was semi-rhetorical. There is no need for word boundaries. The regexp in the pattern attribute is matched against the entire input.

anubhava Over a year ago

Word boundaries are needed otherwise it will match D-DDDD in DDD-DDDD

user663031 Over a year ago

no, because as I said, values of the pattern attribute have implicit anchors.

maioman · Accepted Answer · 2016-09-04 15:02:30Z

0

Another simple alternation example:

/^\w-\w{4}$|^\w{2}-\w{3}$/

answered Sep 4, 2016 at 15:02

maioman

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1 Comment

user663031 Over a year ago

Yes, but the anchors are not necessary.

user663031 · Accepted Answer · 2016-09-04 19:47:21Z

0

It might be slightly shorter to write

/\w(-\w|\w-)\w{3}/

answered Sep 4, 2016 at 19:47

user663031

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