Apply, Call, This and That

fun.js

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

console.log( add.apply(null, [1, 2, 3]) );
// 6

console.log( add.call(null, 2, 3, 4)  );
// 9

var myObject = {
  x: 81,
  whatIsThisX: function (y){
    return [this.x, y];
  }
}

console.log( 'original this: ', myObject.whatIsThisX(64) );
// [81, 64]

console.log( 'replaced this: ', myObject.whatIsThisX.bind({x:9})(4)  );
// [9, 4]

console.log( 'call: ', myObject.whatIsThisX.call({x:5}, 45) );
// [5, 45]

console.log( 'bind: ', myObject.whatIsThisX.bind({x:10}, 12)() );
// [10, 12]

console.log( 'apply: ', myObject.whatIsThisX.apply({x:6}, [39]) );
// [6, 39]