IIFE

Immediately Invoked Function Expression

An IIFE is a javascript function that runs as soon as it is defined.

(function () {
    statements
})();

1. First grouping () is anonymous function which prevents accessing variables and pollutting the global scrope.
2. Second part creates the immediately invoked function express, which the js engine will directly interpret the function

(function () {
    var aName = "Barry";
})();
// Variable aName is not accessible from the outside scope
aName // throws "Uncaught ReferenceError: aName is not defined"

Assigning IIFE to a variable stores the functions's return value.

var result = (function () {
    var name = "Barry"; 
    return name; 
})(); 
// Immediately creates the output: 
result; // "Barry"