When submitting a form for JavaScript validation what does the return before the function call do?

Question

<form name="myForm" action="demo_form.asp" onsubmit="return validateForm();" method="post">

为什么validateForm()之前必须有return ？

Answer 1

If you don't use return , Javascript will call validateForm but will throw away the return value.

If onsubmit returns false the form won't be submitted.

Answer 2

The default submit action of the <form> can be stopped if the onsubmit function returns false .

The value of the onsubmit attribute is treated like a function body, so the return is needed so that the form isn't submitted if it's not valid.

Answer 3

Basically, what's happening in that inline handler is this:

<button id="submit-button" type="submit" onclick="return validate()"></button>

var button = document.getElementById("submit-button");

button.onclick; // function () { return validate(); }

Versus:

<button id="submit-button" type="submit" onclick="validate(event)"></button>

var button = document.getElementById("submit-button");

button.onclick; // equals function (event) { validate(event); }