Limiting the contents of a string via RegEx

Often, you will need to prevent users from entering data that doesn’t conform to a specific pattern. For example, you may want to allow users to enter only numbers or only valid email addresses. To this end, I’ve written a little utility function that returns the “standardised” version of a string, according to the regex you supply.

[sourcecode language=”javascript”]String.implement({
limitContent: function(allowedRegex) {
return $splat(this.match(allowedRegex)).join(”);
}
});[/sourcecode]

Basically, the function takes the result of evaluating the regular expression on the string, converts it into an array if it isn’t one, and then joins the array’s elements together with an empty string.

Examples:

[sourcecode language=”javascript”]console.log(“12345”.limitContent(/.{4}/)); // Only allow four characters
console.log(“joe@mail.com”.limitContent(/[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}/)); // Only allow email addresses
[/sourcecode]