奇怪的JavaScript分配语法的说明

Question

I was reading an article explaining function prototyping and inheritance in JavaScript when I came across these lines of code I can't wrap my head around

a = {} 
(function(){}())

What exactly do these lines do?

Answer 1

a = {} // Be 'a' an empty object (But why ?)

function(){   // Declare a function that says Hello when it's called
   alert("Hello");
}

function(){   // Declare a function that says Hello and execute it immediately with ()
   alert("Hello");
}()

function(){}()   // Declare a function that...does nothing, and execute it immediately with ()... But apparently you can't, that's a syntax error (Thanks @pointy)

(function(){}()) // Makes it work (no syntax error)