Was looking at some decompiled code from ES6 the other day, when I saw a line that looked like this:

var x = (0, anObject.aFunc)(params);

WTF? I had never seen syntax like this before in JavaScript. Time to dig into the docs.

Paraphrasing from Mozilla and StackOverflow:

When you write expressions separated by a comma (,) JavaScript evaluates all the expressions in order and returns the value of the last expression.

Meaning the expression (x=1, y=2, anObject.aFunc) would set the variables x and y, and return anObject.aFunc to the caller.

Now that we know what is going on, why?

Here is the explanation I cobbled together from the Interwebs:

When you call anObject.aFunc(), this is equal to anObject because aFunc is coupled to anObject.

When you call (0, anObject.aFunc)(), you have decoupled aFunc from anObject, so this is no longer equal to anObject in aFunc.

In this case, this would be equal to the global object - window in the browser, or global in node.

So in the example given above:

var x = (0, anObject.aFunc)(params);

Code that would have the same output (in the browser):

var x = anObject.aFunc.call(window, params);

Or, even more trivially:

var boundToWindow = anObject.aFunc;
var x = boundToWindow(params);