javascript limit text input characters

Question

I am wanting to restrict the input characters for a text box to [a-z0-9_-]. However whenever if do this buttons like backspace and the arrow keys don\'t work. I have found s

Answer 1

You haven't provided any code samples, so it's hard to be specific in a response, but as a general strategy, try this: instead of trying to whitelist characters that can be input while they are being typed in, validate the contents of the text box after every key stroke to make sure that it still contains valid characters. If it doesn't, remove the last character entered.

This approach will allow special keys like backspace, etc., while at the same time achieve what it sounds like you are really after: a valid value in the text box.

Answer 2

Just change the regex in the example to something like this:

numcheck = /[^a-z0-9_-]/;

Or better yet, avoid the double negative with:

numcheck = /[a-z0-9_-]/;
return numcheck.test(keychar);

Then you can look up the keycodes of backspace, etc. and check for them too:

if (keychar === 8) return true;
...

Or even put them in your regex:

numcheck = /[a-z0-9_\x08-]/;

Answer 3

Add this code to onkeypress event.

    var code;
    document.all ? code = e.keyCode : code = e.which;
    return ((code > 64 && code < 91) || (code > 96 && code < 123) || code == 8 || code == 32 || (code >= 48 && code <= 57));

For browser compatibility, You can add var k = e.keyCode == 0 ? e.charCode : e.keyCode;

Answer 4

Yes you can limit the input of characters. For example create a function that checks what is going on, return true if everything is OK and false if not:

// return true for 1234567890A-Za-z - _
function InputCheck(e) {
    if ((e.shiftKey && e.keyCode == 45) || e.which != 8 && e.which != 0 && (e.which < 48 || e.which > 57)) {
        if (e.which == 45 || e.which == 95 || (e.which >= 65 && e.which <= 90) || (e.which >= 97 && e.which <= 122))
            return true;
        return false;
    }
    return true;
}

once you have the function, hook it into you input (this is with jQuery):

$('#InputID').keypress(InputCheck);

You can make as complicated a check as you want, for example this will allow for USD money values:

function InputCheck(e) {
    if ((e.shiftKey && e.keyCode == 45) || e.which != 8 && e.which != 0 && (e.which < 48 || e.which > 57) && e.which != 46 && e.which != 36) {
        return false;
    }
    // . = 46
    // $ = 36
    var text = $(this).val();

    // Dollar sign first char only
    if (e.which == 36 && text.length != 0) {
        return false;
    }

    // Only one decimal point
    if (e.which == 46 && text.indexOf('.') != -1) {
        return false;
    }

    // Only 2 numbers after decimal
    if (text.indexOf('.') != -1 && (text.length - text.indexOf('.')) > 2) {
        return false;
    }

    return true;
}

Answer 5

You can press any key you like, as long as you keep the value from including anything not in the white-list.

inputelement.onkeyup=function(e){
  e=e || window.event;
  var who=e.target || e.srcElement;
  who.value= who.value.replace(/[^\w-]+/g,'');
}