How can I use a regex in javascript?

Question

I found a regex at regexlib and I want to use it in a simple string validation using javascript.

The regex is:

^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$

But I tried to use it like this:

mystring = '[email protected]';
re = '^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$';

    if(mystring.match(re)){
     console.log('true');
    }

And I got this console error:

Uncaught SyntaxError: Invalid regular expression: //^([a-zA-Z0-9_-.]+)@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.)|(([a-zA-Z0-9-]+.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(]?)$/: Range out of order in character class

What's wrong? I'm not a professional.. This is just a simple project I'm trying to do in my free time.

Possible duplicate of Range out of order in character class in javascript — pushkin
– pushkin, Commented Apr 30, 2018 at 2:29
When I 'try to follow this another post solution I get another error: Uncaught SyntaxError: Invalid or unexpected token — Russel Riehle
– Russel Riehle, Commented Apr 30, 2018 at 2:33

Cory Kleiser · Accepted Answer · 2018-05-03 08:04:13Z

Try doing it like this:

var re = new RegExp('^([a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([a-zA-Z0-9\\-]+\\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?)$');

In javascript the \ character escapes the string so that's why it's not working. In the previous example I just doubled them up and that should work. Here it is in practice:

mystring = '[email protected]';
re = new RegExp('^([a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([a-zA-Z0-9\\-]+\\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?)$');

if (mystring.match(re)) {
  console.log('true');
}

You could also try a RegEx literal like this:

var re = /^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;

Here is that in practice:

var mystring = '[email protected]';
var re = /^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;

if (mystring.match(re)) {
  console.log('true');
}

Intervalia · Accepted Answer · 2018-04-30 02:34:44Z

2

To define a RegEx you need to use / and not '.

mystring = '[email protected]';
re = /^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;

    if(mystring.match(re)){
     console.log('true');
    }

answered Apr 30, 2018 at 2:34

Intervalia

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