invalid regex javascript

Question

Can you explain me why this regex is invalid ?

new RegExp("^(0|\+33)+[0-9]{9}$");

Validate by regex online

with regex online you don't have to worry about the string escapes in addition to regex escapes. That's why it works with regex online but not in this example, because you're constructing the RegExp with a string. As @MarkMeyer said, if you use a regex literal you won't run into the string escape problem. — David784
– David784, Commented Jul 2, 2019 at 21:34

David784 · Accepted Answer · 2019-07-02 21:42:49Z

3

You need a double backslash before the first +, like this:

new RegExp("^(0|\\+33)+[0-9]{9}$");

When JavaScript evaluates the string, it reads \+ as simply +. Then the RegExp sees |+, which is two Regex operators back to back (or and repeat 1 to infinite times)...which is invalid.

edited Jul 2, 2019 at 21:42

answered Jul 2, 2019 at 21:30

David784

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5 Comments

Get Off My Lawn Over a year ago

You forgot the double backslash.

David784 Over a year ago

@GetOffMyLawn thanks, I got in too much of a hurry. Fixed now

Matthis.h Over a year ago

Invalid regular expression: /^(0|+33)+[0-9]{9}$/: Nothing to repeat

David784 Over a year ago

@Matthis.h not sure what browser you're using, but I just copied and pasted my code into Chrome/75.0.3770.90 console, and it worked perfectly. Returned this: /^(0|\+33)+[0-9]{9}$/

Matthis.h Over a year ago

I'm using Chrome 75.0.3770.100

Dez · Accepted Answer · 2019-07-02 21:43:19Z

1

Your regex work as expected with regex literals. With the string literals you need to double escape the special chars.

const r = /^(0|\+33)+[0-9]{9}$/;
console.log(r.test('0782896736'));
console.log(r.test('+33782896736'));
console.log(r.test('blabla'));


const regexp = new RegExp('^(0|\\+33)+[0-9]{9}$');
console.log(regexp.test('0782896736'));
console.log(regexp.test('+33782896736'));
console.log(regexp.test('blabla'));

answered Jul 2, 2019 at 21:43

Dez

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