How to prevent user from entering special characters in text box when length is 0?

Question

I have the following code which prevents user from entering space when the length is 0. Now, how can I prevent user from entering all special characters(anything other than

Answer 1

The letter and digit ranges are (inclusive):

• 97 - 122 (a-z)
• 65 - 90 (A-Z)
• 48 - 57 (0-9)

This is what you compare e.which against.

if (e.which < 48 || 
    (e.which > 57 && e.which < 65) || 
    (e.which > 90 && e.which < 97) ||
    e.which > 122) {
    e.preventDefault();
}

Or, using inverse logic:

var valid = (e.which >= 48 && e.which <= 57) || (e.which >= 65 && e.which <= 90) || (e.which >= 97 && e.which <= 122);
if (!valid) {
    e.preventDefault();
}

Update

Even so, you may still wish to validate the field contents as a whole using a regular expression:

if (/^[A-Z0-9]+$/i.test(value)) {
    // it looks okay now
}

Or fix the field by replacing the bad stuff:

var stripped = value.replace(/[^A-Z0-9]+/i, '');