iife.md

Explain why the following doesn't work as an IIFE: function foo(){ }();

This is a function definition, it defines foo. But it’s not a function expression - that is, it’s not understood by the JS parser to actually call a function.

For the parser, things look like this:

function foo(){
} // ok, done with that function definition
  // (silly human left off the semicolon, how embarrassing!)

(); // Are they trying to call something? What’s the function’s name?
    // PARSE ERROR

In order to prep the parser that we're actually dealing with a function expression we have to wrap things up in () like so:

( // oh goody, we're going to call some function expressions!
  function foo(){ // here's the function definition
  }() // and here's where the function is actually called
);