Part of RegExp pattern from variable

Question

I am a newbie in regular expressions. I have a problem with this one. I need to add chars from addons variable as allowed characters to the next regex re.

var addons = '_-';
re = new RegExp(/^[a-zA-Z]+$/i);

console.log('match a', re.test('a'));
console.log('match a_', re.test('a_'));
console.log('no match 9', re.test('9'));
console.log('no match 9_', re.test('9_'));

Any suggestions? Thanks.

Are the addons characters only allowed at the end? Or in any position? — Robby Cornelissen
– Robby Cornelissen, Commented Nov 11, 2014 at 9:42

Scimonster · Accepted Answer · 2014-11-11 09:40:02Z

1

You need to construct the regex allowing those characters too:

var addons = '_-';
    re = new RegExp('^[a-zA-Z]+['+addons+']?$','i');

console.log('match a', re.test('a'));
console.log('match a_', re.test('a_'));
console.log('no match 9', re.test('9'));
console.log('no match 9_', re.test('9_'));

That will test for any of the characters in addons (the brackets), and they're not required (the ?).

answered Nov 11, 2014 at 9:40

Scimonster

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