Question

I have this code, but somewhy when i use this function to validate my input field everything works, except + and – keys, even thought i noted them as true. What have i done wrong?

function validateNumber(event)
{
    var key = window.event ? event.keyCode : event.which;

    if (event.keyCode == 8 || event.keyCode == 46 || event.keyCode == 37 ||
        event.keyCode == 39 || event.keyCode == 107 || event.keyCode == 109 ||
        event.keyCode == 32 )
    {
        return true;
    }
    else if(key < 48 || key > 57)
    {
        return false;
    }
    else return true;
};

Answer 1

I don’t see you checking for 189 (-) and 187 (=, which is really what happens when you type +). You might want to check if the Shift key is pressed for +.

As already noted, it’s overall a wrong way to validate user input. You need to inspect the value of the input, not individual keystrokes.

First, define a validation function that would check an arbitrary text with a regexp:

function checkArithmetic(str) {
    var regexp = /^[0-9+-]$/;
    return regexp.test(str);
}

Next, add a handler to your input element:

input.addEventListener('input', function (e) {
    var value = input.value;

    if (checkArithmetic(value)) {
        // OK!
    } else {
        // error
    }
}, false);