How to call a JavaScript function on submit form?

The onsubmit event occurs when you try to submit a form. You can put your form validation against this event type. The following example shows how to use onsubmit. Here we are calling a validate() function before submitting a form data to the webserver. If validate() function returns true, the form will be submitted, otherwise it will not submit the data.

      function validation() {
         all validation goes here
         return either true or false

The HTML code snippet.

<form method="POST" action="new.cgi" onsubmit="return validate()">
   <input type="submit" value="Submit" />