Instantanious Form Field Multiplication

[EnriqueI]

How would I have two fields in a form multiply each other instantaneously inputing the result into a third field, that the user can not edit? I can do this with javascript, but I need a button to trigger it.

[tibberous]

Fire it off the on change event of the inputs, not the buttons click event.

[EnriqueI]

Fire it off the on change event of the inputs, not the buttons click event.

 

Change the javascript to calculate on change of the inputs? How would I do that? (sorry, I'm a newbie to anything web development... or coding in general.)

[tibberous]

<script>
function update(){
document.getElementById('answer').value = document.getElementById('f1').value * document.getElementById('f2').value;
}
</script>
<input id='f2' type='text' onchange='update()'><input id='f1' type='text' onchange='update()'><input id='answer' type='text'>

[EnriqueI]

<script>
function update(){
document.getElementById('answer').value = document.getElementById('f1').value * document.getElementById('f2').value;
}
</script>
<input id='f2' type='text' onchange='update()'><input id='f1' type='text' onchange='update()'><input id='answer' type='text'>

 

Thanks.

[discomatt]

Might as well just update the innerHTML of a span... that way there's no editing anyways