javascript return true 或 return false 什么时候用，怎么用？

Question

So I see a lot of JavaScript code (have written some myself) that does something like

<script>
function CallSomeFunction()
{
   //function body
}

$(document).ready(function () {
 callSomeFunction();
 return false;
});

and at other times:

callSomeFunction();
return true;

Basically I've never understood the true use of the return true/false after function calls in JavaScript. I've just assumed its some kind of magic I need my functions to run well.

So please I'd like to know why? why do we use return true or return false after calling a JavaScript function?

Answer 1

I think a lot of times when you see this code, it's from people who are in the habit of event handlers for forms, buttons, inputs, and things of that sort.

Basically, when you have something like:

<form onsubmit="return callSomeFunction();"></form>

or

<a href="#" onclick="return callSomeFunction();"></a>`

and callSomeFunction() returns true, then the form or a will submit, otherwise it won't.

Other more obvious general purposes for returning true or false as a result of a function are because they are expected to return a boolean.

Answer 2

Your code makes no sense, maybe because it's out of context.

If you mean code like this:

$('a').click(function () {
    callFunction();
    return false;
});

The return false will return false to the click-event. That tells the browser to stop following events, like follow a link. It has nothing to do with the previous function call. Javascript runs from top to bottom more or less, so a line cannot affect a previous line.

Answer 3

returning true or false indicates that whether execution should continue or stop right there. So just an example

<input type="button" onclick="return func();" />

Now if func() is defined like this

function func()
{
 // do something
return false;
}

the click event will never get executed. On the contrary if return true is written then the click event will always be executed.

Answer 4

This works for me:

<form action="javascript:void(0);" onsubmit="return checkForm(this);">

Answer 5

People often use a variable's Boolean value to determine whether or not it was properly defined.
Similarly, it's occasionally used to confirm that a function was completed successfully.

When writing a method that doesn't return anything, it's good practice to return a true value anyway.
This could be substituted for any other value deemed “truthy”, like 1 or a non-empty string.

For example, if I wrote “console.log('Hello, ') && console.log('World!');”, only the first log would appear, since console.log doesn't return true (at least in my IDE). If it did, both would appear.
Of course, this extends to any Boolean-related operation, like if-else statements, switches, and ternary.

Regarding the web example, I'm pretty sure jQuery uses the aforementioned system for cycling through DOM event listener callbacks.