isNaN function on a textbox in a form

[myza123]

I am using HTML and JS to make a form, but one of the text boxes needs to validate that it will only accept digits as it is for a number, but I can't figure out how to do this with the isNaN function.
PS it also has to be exactly four digits long

Any help would be appreciated thanks

[Dormilich]

HTML5 solution

<input type="number">

if number boxes are not supported:

// 'input' be the text box DOM element
if (isNaN(input.value)) {
    // validation failed
}

[myza123]

ok, but now when i click submit with only numbers in the textbox, it still shows the dialog saying you must enter digits only

[Dormilich]

show your code.