如何防止用户在长度为0时在文本框中输入特殊字符？

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 az AZ 0-9) when the length is 0?

$('#DivisionName').bind('keypress', function(e) {
    if($('#DivisionName').val().length == 0){
        if (e.which == 32){//space bar
            e.preventDefault();
        }
    }
}); 

This is my text box.

<input type="text" id="DivisionName" />

Answer 1

The letter and digit ranges are (inclusive):

• 97 - 122 (az)
• 65 - 90 (AZ)
• 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, '');

Answer 2

This is what you are looking for:

$('#DivisionName').bind('keypress', function(e) {

    if($('#DivisionName').val().length == 0){
        var k = e.which;
        var ok = k >= 65 && k <= 90 || // A-Z
            k >= 97 && k <= 122 || // a-z
            k >= 48 && k <= 57; // 0-9

        if (!ok){
            e.preventDefault();
        }
    }
}); 

or see here: http://jsfiddle.net/D4dcg/

Answer 3

You can use a regex to validate the string. Something like ^[a-zA-z0-9].*

Here is an article about testing a regex in javascript : http://www.w3schools.com/jsref/jsref_regexp_test.asp

And you can even bind a change event and not a keypress.