Hiding in Plain Scope

• You can hide variables and functions by enclosing them in the scope of a function.
• Inspired by the Principle of Least Privilege which states that you should expose only minimally and hide everything else.

• Another benefit of hiding variables and functions is to avoid unintended collision of identifiers.

  function doSomething(a) {
    b = a + doSomethingElse( a * 2 );
    console.log( b * 3 );
  }
    
  function doSomethingElse(a) {
    return a - 1;
  }
    
  var b;
    
  doSomething( 2 ); // Output 15
  

The b variable and doSomethingElse(..) can be treated as private details of doSomething(..) function.

Proper Design

function doSomething(a) {
  function doSomethingElse(a) {
    return a - 1;
  }

  var b;

  b = a + doSomethingElse( a * 2 );

  console.log( b * 3 );

}

doSomething( 2 ); // Output 15

Global Namespace

Multiple libraries can collide with each other. To avoid such collision, such libraries will create a single variable declaration (often an object) with significantly unique name, in the global scope.

This object is then used as a namespace for that library, where all specific exposures of functionality are made as properties off that object.

var MyBestJSLibrary = {
  awesome: "stuff",
  doSomething: function() {
    //..
  },
  doAnotherThing: function() {
    //..
  }
};

Reference: Scope & Closures By Kyle Simpson