Question

As others recommended “create a whitelist” but I really wanted to create a blacklist.
this is my code

if($("#txtTag").val().length <=0 || $("#txtTag").val() =="")
{
    $("#ep-insert-keyword").html("Please Enter Keyword");
    $("#ep-insert-keyword").fadeIn("normal");
}
else if(!RegexCheck(/^[a-zA-Z\_]+$/g,$("#txtTag").val()))
{
    $("#ep-insert-keyword").html("Special characters are not allowed");
    $("#ep-insert-keyword").fadeIn("normal");
}

I want to prevent my users to enter any special character I defined in my regex.
the characters i want to prevent are this ranges of characters in ASCII

0-47 58-64 91-96 123-127

I really want to reverse my code from whitelist to BLACKLIST… but i don’t know how.

I don’t worry about other languages as i really want them to pass my validation… i just want to block the characters on the ASCII ranges i wanted

Answer 1

Though I’m with the others and recommend a whitelist, here’s how you would do a blacklist using a regex:

// 0-47 : 00-2F : control codes, spaces, punctuation
// 58-64 : 3A-40 : more punctuation
// 91-96 : 5B-60
// 123-127 : 7B-7F

function verifyChars(str) {
    return str.match(/^[^\x00-\x2F\x3A-\x40\x5B-\x60\x7B-\x7F]+$/) != null;
}

And here’s a jsFiddle with a bunch of test cases in it: http://jsfiddle.net/jfriend00/24xF7/

Or a little more efficient (because it only evaluates the regex once at startup and uses .test()):

var verifyChars = (function() {
    var re = /^[^\x00-\x2F\x3A-\x40\x5B-\x60\x7B-\x7F]+$/;
    return function(str) {
        return re.test(str);
    }
})();

jsFiddle of this one with test cases: http://jsfiddle.net/jfriend00/fZ3AN/

FYI, here’s a good reference on how to put unprintable chars into a regex: http://www.regular-expressions.info/characters.html