Because JavaScript is a functional object-oriented language, functions can have methods. The "apply" methods lets us construct an array of arguments to use to invoke a function. It also lets us choose the value of "this". The "apply" methods takes two parameters. The first is the value that should be bound to "this". The second is an array of pa…

the_apply_invocation_pattern.js

add = function(a, b){ return a + b; };

//Make an array of 2 numbers and add them.

var array = [3, 4];
var sum   = add.apply(null, array); //sum is 7

console.log(sum);

/*----------------------------------------*/
var Quo = function(string){ this.status = string; };
Quo.prototype.getStatus = function( ){ return this.status; };

//Make an object with a status member.

var statusObject = {
  status: 'A-OK'
};

//statusObject does not inherit from Quo.prototype,
//but we can invoke the get_status method on statusObject
//even though statusObject does not have a getStatus method.

var status = Quo.prototype.getStatus.apply(statusObject);

console.log(status); //Show 'A-OK'