javascript validation

I have two input fields say val1 and val2开发者_开发百科 in jsp.Let say val1 is dynamic, I need to restrict user entering the value of val2 not exceeding val1. It can be equal but not more. I tried with onKeypress but i was not able to success. Val1 value can be get from document.getElementById(..).value. Can anyone tell me the efficient way to do this. Thanks

Use the onChange event.

<script>
function checkValues(in) {
    var val1 = getElementById(val1);
    var val2 = getElementById(val2);

    // Don't check if values are missing
    if (val1.value == "" || val2.value == "") return;

    // Don't allow val2 to be greater than val1
    if (parseInt(val1.value) 
            > parseInt(val2.value)) {
        // Try not to use an alert, replace this with an in-page warning.
        alert("Value 2 must be greater than Value 1.");
        in.value = "";
    }
}
</script>
<input type="text" id="val1" onChange="checkValues(this)" />
<input type="text" id="val2" onChange="checkValues(this)" />

Note that this doesn't fully stop a user from submitting an invalid value. You should also verify the values on the server

Do something like this in client side javascript.

if (document.getElementById('val1').value.length <= document.getElementById('val2').value.length)