Question

When typing into a <input type="text"> field I would like to precheck every entered value before it appears on the screen. E.g. if the user enters any non numeric value, nothing will happen and only if he enters a numeric value the field will change.

Which is the right event to use keydown(), keyup() or is there something better? How do I cancel the current change of the text field without having to remember the old value and manually resetting it?

Answer 1

You could bind to the keypress event and then check the character represented by the which property of the event object. If it isn’t a number you can use preventDefault to prevent the default behaviour of writing the character to the element:

$("#someInput").keypress(function(e) {
    if(isNaN(String.fromCharCode(e.which))) {
        e.preventDefault();
    }
});

Here’s a working example.