Question

After reading both :

difference between "void 0 " and "undefined" , https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/void

I still have some questions.

I’ve read that
window.undefined can be overwritten vwhere void operator will return the undefined value always

But the example which caught my eyes was the one in MDN :

<a href="javascript:void(0);">Click here to do nothing</a>

In order to do nothing , I always thought I should write :

href="javascript:return false;"

And this leads me to another question : (at Href context !) :

javascript:void(0); vs javascript:return false;

What is the differences ?

Also – Does

function doWork() {
    return void( 0 );
}

is exactly

function doWork() {

    return undefined;
}

Thanks.

Answer 1

This will not work properly:

href="javascript:return false;"

because you are not in a function. You are thinking of this:

onclick="return false;"

which is correct since return false; is placed in a function. The false value tells the onclick to prevent the default behavior of the element.

For the return statement to work in an href attribute, you’d need a full function.

href="javascript:(function() { return false; })();"

but that’s just long and ugly, and as the comments note, JavaScript in an href is generally discouraged.

EDIT: I just learned something. Having a non undefined expression as above seems to replace the elements with the return value (at least in Firefox). I’m not entirely familiar with the full ramifications of using JavaScript in an href, because I never do it.

---

Yes, this:

return undefined;

returns exactly the same thing this:

return void 0;

as long as the undefined variable has not been redefined or shadowed by some other value.

But while they may return the same thing, it’s not entirely accurate to say they are the same thing, because:

• undefined is a global variable whose default value is the undefined primitive

• void is an unary operator that will replace the return value of its operand with the undefined primitive

So they both result in the undefined primitive, but they do so in a very different way.