Question

I’m trying to use the following code with jQuery to validate hex value strings but I get unexpected results:

var a = new RegExp("0x[a-fA-F0-9]+")
var result = a.test('0x1n')

In this case, result actually returns true. What am I missing here?

Answer 1

You need anchors to match the beginning and the end of the string. This will make the regular expression try to match against the entire string instead of just a part of the string:

var a = new RegExp("^0x[a-fA-F0-9]+$")

Otherwise your regular expression matches the 0x1 part and returns true.

On another note, the following would be a little better:

var re = /^0x[a-f0-9]+$/i;

The i flag makes it case insensitive so you don’t have to specify a-f and A-F.