Javascript regular expression - string to RegEx object

Question

I am sure its something pretty small that I am missing but I haven't been able to figure it out.

I have a JavaScript variable with the regex pattern in it but I cant seem to be able to make it work with the RegEx class

the following always evaluates to false:

var value = "[email protected]";
var pattern = "^\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}$"
var re = new RegExp(pattern);
re.test(value);

but if I change it into a proper regex expression (by removing the quotes and adding the / at the start and end of the pattern), it starts working:

var value = "[email protected]";
var pattern = /^\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}$/
var re = new RegExp(pattern);
re.test(value);

since I always get the pattern as a string in a variable, I haven't been able to figure out what I am missing here.

RoToRa · Accepted Answer · 2011-01-04 00:14:58Z

32

Backslashes are special characters in strings that need to be escaped with another backslash:

var value = "[email protected]";
var pattern = "^\\w+@[a-zA-Z_]+?\\.[a-zA-Z]{2,3}$"
var re = new RegExp(pattern);
re.test(value);

answered Jan 4, 2011 at 0:14

RoToRa

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2 Comments

omg I knew it was something pretty simple that i was missing. Thanks!!

It isn't pretty simple if you change the example.