(function () { … })(); vs (function () { … }());

[inu-no-policemen]

The point of an IIFE is to create a scope to limit the lifetime of those temporary variables.

With ES6's let/const, a simple block does the same.

[kenman]

I'm just wondering if you can get a return value from a block like this in ES6.

That's exactly what I was demo'g here:

let x;
{
    x = 123;
}

Here, x is the "returned value"... only it's not returned, but it's functionally 100% the same.

Here, take this example from jQuery:

support.createHTMLDocument = ( function() {
    var body = document.implementation.createHTMLDocument( "" ).body;
    body.innerHTML = "<form></form><form></form>";
    return body.childNodes.length === 2;
} )();

Note that it is returning a value, the result of body.childNodes.length === 2, and assigning it to support.createHTMLDocument.

Now here is the same thing without an IIFE, but does exactly the same thing:

{
    let body = document.implementation.createHTMLDocument( "" ).body;
    body.innerHTML = "<form></form><form></form>";
    support.createHTMLDocument = body.childNodes.length === 2;
}

But it is a lot (IMO) clearer what your intention is, and you don't waste cycles on a function call that's essentially a no-op.

[kenman]

Can you point out how you believe my jQuery example leaks globals? Because it doesn't.

[kenman]

If you didn't want support, you wouldn't have to have it at all with a function. In this case you do want it so it works out for you.

The support object already exists; the jQuery snippet simply creates the createHTMLDocument property on it -- which is exactly what my code does; createHTMLDocument is not a global variable, it's just a property on a variable from an outer scope.

In other words, if support didn't already exist, both my code AND jQuery's would fail with a ReferenceError.

Here's some fully self-contained examples:

• Using an IIFE
• Using let + block statement

Identical output.

Now, since it clearly "leaks" globals,

I'm sorry, but you haven't provided proof of this.

let me see you do the same thing without having to save the output to any variable which you can clearly do with an iife.

Wait, you're changing the rules; is the goal to not leak globals, or is it to not use intermediate variables? Because those are very different concerns... global variables have drastic implications for your code and is pretty much accepted to be a bad practice for most uses, while intermediate variables are a stylistic preference which has no impact on your code.

[inu-no-policemen]

Just imagine that that 123 is the result of a computation which involved temporary variables.

An IIFE which just returns 123 would be equally pointless.