The onChange Event

The onChange event is particularly useful when it's applied to a form. This event will fire whenever a form is updated.

It's implemented as follows:

    <form  id="carRental">
            <p>Extra Car Cleaning Services?</p>    
            <p><input type="checkbox" name="extras" value="wheelCleaning"> Wheel cleaning (£3) </p>
            <p><input type="checkbox" name="extras" value="rustProtection">  Rust protection (£2) </p>
            <p><input type="checkbox" name="extras" value="airFreshner">  Air freshener (£1) </p>
    </form>

HTML

function main() {
    var carRentalForm = document.getElementById("carRental");
    carRentalForm.addEventLinstener("change", formChanged);
}

function formChanged(event) {
    console.log("the form has changed");
    // run some validation 
   // update some information for the user 
}

javaScript