Input which accepts only numbers

by Mauno Vähä

HTML

<form name="myForm">
    <p>Enter numbers only:
        <input type="text" id="deliveryPostcode" />
    </p>
</form>

JavaScript

var postcode = document.getElementById("deliveryPostcode");
postcode.onkeypress = checkForDigits;

function checkForDigits(event) {

    var chCode = ("charCode" in event) ? event.charCode : event.keyCode;

    if (chCode < 48 || chCode > 57) {
        
        alert("Not a digit");
        
        // return false means that letter won't be placed to input
        return false;
    }

}