The (0, func) operation in transpiled code
Figuring out JS quirks
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(),thisis equal toanObjectbecauseaFuncis coupled toanObject.When you call
(0, anObject.aFunc)(), you have decoupledaFuncfromanObject, sothisis no longer equal toanObjectinaFunc.In this case,
thiswould be equal to the global object -windowin the browser, orglobalin 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);