Problems with dynamic RegExp construction in Javascript

Question

This method is to prevent users from entering anything but numbers and "allowed characters." Allowed characters are passed as the parameter allowedchars.

So far, the method prevents number entries but the allowedchars doesn't work (tried with passing "-" (hyphen) and "." (period)). So I'm assuming my dynamic regex construction isn't correct. Help?

Thanks in advance!

numValidate : function (evt, allowedchars) {
    var theEvent, key, regex,
    addToRegex = allowedchars;

    theEvent = evt || window.event;
    key = theEvent.keyCode || theEvent.which;
        key = String.fromCharCode(key);
        var regex = new RegExp('/^[0-9' + addToRegex + ']$/');
        if (!regex.test(key)) {
            theEvent.returnValue = false;
            if (theEvent.preventDefault) {
                theEvent.preventDefault();
            }
        }
}

(ps. jQuery solutions are fine too)

kennytm · Accepted Answer · 2010-09-19 07:35:10Z

2

1. When you construct via new RegExp, there's no need to include the surrounding /s.

    var regex = new RegExp('^[0-9' + addToRegex + ']$');

2. But if addToRegex contains ] or -, the resulting regex may become invalid or match too much. So you need to escape them:

    var regex = new RegExp('^[0-9' + addToRegex.replace(/([\-\]])/g, '\\$1') + ']$');

3. But since you are checking against 1 character anyway, it may be easier to avoid regex.

    var pass = ("0123456789" + addToRegex).indexOf(key);
    if (pass == -1) {
      ...

answered Sep 19, 2010 at 7:35

kennytm

526k110 gold badges1.1k silver badges1k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Kyle Cureau Over a year ago

Sorry @KennyTM...you are totally right. I thought I had copied and pasted it but chopped out a bracket from the middle, mid-ether. :) I've deleted my prior comment. Thanks for the answer!

Collectives™ on Stack Overflow

Problems with dynamic RegExp construction in Javascript

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related