Self invoking function in JavaScript

Question

I have a self invoking function like this:

var f = (function f(){ return "123"; }, 
         function g(){ return 2; },
         function h(){ return "test"; })();

typeof f;

typeof f is always the type of what is returned in the last function definition. Like if h is last, then it is "string", but if I remove h and have g as last, then "number".

Could someone explain why?

Answer 1

Let's break this down.

The comma operator in Javascript evaluates several expressions, and returns the last one:

>>> "a", 1
1
>>> 1, "a"
"a"

So when you take three anonymous functions and string them together with commas, it evaluates to the last one:

>>> (function f(){ return "123"; }, function g(){ return 2; }, function h(){ return "test"; })
function h(){ return "test"; }

Evaluating that result executes the function, returning "test".

Whichever function is last in the comma-separated list will be executed, and decide the overall return value.