Question

I am using the following regex in .NET to validate that a string contains 12 numeric characters and it works perfectly. (EG: 000000174064)

public static string TwelveDigitNumber = @"^\d{12}$";

However that same regular expression does not work client side using javascript.

EDIT: I am using jquery validate, and have added the following function for regular expresssions

// regex validation
$.validator.addMethod(
        "regex",
        function (value, element, regexp) {
            var re = new RegExp(regexp);
            return this.optional(element) || re.test(value);
        },
        "Please check your input."
);


 rules: {
                    "Number": {
                        maxlength: 12, regex: "^\d{12}$"
                    },

Answer 1

The result from new RegExp( "^\d{12}$" ) is /^d{12}$/ instead of /^\d{12}$/ because of the escape backslash. It works in .NET because you have @ which I think skips the escaping.

Anyway, for static regexes you can just use regex literals:

regex: /^\d{12}$/

is same as

regex: new RegExp( "^\\d{12}$" )

You can then pass it directly to the function and it doesn’t have to instantiate it every time.