JavaScript Events (Cont.)
onSubmit
The onSubmit event executes JavaScript code when a submit event occurs; that is, when a user submits a form.
The isUpper() function will be called when the user clicks on the submit button in the form.
The following script validates the information in the form and only allows it to be submitted if the requirement (lowercase letters only) is met.
The function
isUpper() returns either
true or
false.
If it returns
true, the form will be submitted; otherwise, the submission will be cancelled.
The notation
testform.command.value, a path to find the HTML element, is from DOM (Document Object Model).
Demonstration
The following demonstration shows how the script of HTML and JavaScript is displayed on the Web.