javascript
function makeF() { 
	var x = 11; 
	var y = 22; 
	return function (what) { 
		switch (what) { 
			case "x": 
				return x; 
				
			case "y": 
				return y; 
		} 
	} 
} 

var f = makeF(); 
f("x");

javascript
function outer() {
  var x = HUGE;  // huge object
  function inner() {
    var y = GIANT;  // giant object :-)

    use(x);  // usage of x cause it to be allocated to the context

    function innerF() {
      use(y);  // usage of y causes it to be allocated to the context
    }

    function innerG() {
      /* use nothing */
    }

    return innerG;
  }

  return inner();
}

var o = outer();  // o will retain HUGE and GIANT.

javascript
function f(a) {  // a is context allocated
  var x = 10;  // x is context allocated
  function g(b) {  // b is context allocated
    var y = 10;  // y is context allocated
    function h(c) {  // c is context allocated
      with (obj) {
        z = c;
      }
    }
    h(b);
  }
  g(a);
}

function k(x, y) {  // x and y are context allocated
  return arguments[0] + arguments[1];
}

function sk(x, y) {  // x and y are not context allocated
  "use strict";
  return arguments[0] * arguments[1];
}

javascript
// Classic Object
function ClassicObject() {
  this.x = 10;
}
ClassicObject.prototype.getX = function () {
  return this.x; // (1)
};


// Closure Object
function ClosureObject() {
  var x = 10;
  return {
    getX: function () {
      return x; // (2)
    }
  };
}



var classic_object = new ClassicObject();
var closure_object = new ClosureObject();

// 이제 컴파일과 최적화를 유도하기 위해 루프를 돌린다.
for (var i = 0; i < 1e5; i++) classic_object.getX();
for (var i = 0; i < 1e5; i++) closure_object.getX();

assembly
mov eax, [ebp+0x8]     ;; 스택에서 this를 로드
mov edx, eax           ;; receiver를 edx에 둠
mov ecx, "x"           ;; 프로퍼티 이름을 ecx에 둠
call LoadIC_Initialize ;; IC 스텁 호출

assembly
test_b dl, 0x1              ;; receiver가 smi가 아닌 객체인지 확인
jz miss                     ;; 아니면 miss로 이동
cmp [edx-1], 0x2bb0ece1     ;; 객체의 hidden class 확인
jnz miss                    ;; 아니면 miss로 이동
mov eax, [edx+0xb]          ;; IC 히트, 고정 오프셋으로 필드 로드
ret
miss:
jmp LoadIC_Miss             ;; miss 처리 위해 런타임으로 점프

assembly
;;; @11: gap.
mov eax,[ebp+0x8] ;; this 가져오기
;;; @12: check-non-smi.
test eax,0x1 ;; smi(숫자 같은 원시값) 인지 아닌지 체크
jz 0x3080a00a        ;; deoptimization bailout 1
;;; @14: check-maps.
cmp [eax-1],0x2bb0ece1
jnz 0x3080a014       ;; deoptimization bailout 2
;;; @16: load-named-field.
mov eax,[eax+0xb]
;;; @18: return.
mov esp,ebp
pop ebp
ret 0x4

assembly
[Start]
  |
  v
this 로드 (eax = this)
  |
  v
check-non-smi: eax가 Smi(원시값)인지 가드 (객체가 아니라 원시값이면 프로퍼티 읽으면 안됨!)
  |Yes ----------------------> [DEOPT] (비최적화 코드로 되돌아감)
  |
  No
  |
  v
check-maps: eax의 hidden class(map)가 예상값인지 가드
(예상했던 hidden class 가 아니라면 고정 오프셋 쓰면 안됨!)
  |No -----------------------> [DEOPT]
  |
  Yes
  |
  v
load-named-field: eax = *(eax + offset_of_x)
  |
  v
return eax

javascript
functionClassicObject() {
	this.x =10;
	this.y =20;
}

ClassicObject.prototype.getSum = function () {
	returnthis.x +this.y;
};

assembly
;;; @11: gap.
mov eax,[ebp+0x8]
;;; @12: check-non-smi.
test eax,0x1
jz 0x5950a00a
;;; @14: check-maps.
cmp [eax-1],0x24f0ed01
jnz 0x5950a014
;;; @16: load-named-field.
mov ecx,[eax+0xb]
	;;; @18: load-named-field.
mov edx,[eax+0xf]

assembly
[Start]
  |
  v
this 로드 (eax = this)
  |
  v
check-non-smi (this가 객체인가?)
  |Fail ---------------------> [DEOPT]
  |
  Pass
  |
  v
check-maps (this의 map이 예상한 구조인가?)
  |Fail ---------------------> [DEOPT]
  |
  Pass
  |
  v
x 로드 (ecx = *(eax + offset_of_x))
  |
  v
y 로드 (edx = *(eax + offset_of_y))
  |
  v
(+ 연산 수행: ecx + edx)
  |
  v
return

javascript
mov eax, esi            ;; 컨텍스트를 eax로 이동
mov eax, [eax + 0x17]   ;; 컨텍스트의 고정 오프셋에서 변수 로드

javascript
// Classic Object
function ClassicObject() {
  this.x = 10;
  this.y = 20;
}
ClassicObject.prototype.getSum = function () {
  return this.getX() + this.getY();
};
ClassicObject.prototype.getX = function () { return this.x; };
ClassicObject.prototype.getY = function () { return this.y; };


// Closure Object
function ClosureObject() {
  var x = 10;
  var y = 10;
  function getX() { return x; }
  function getY() { return y; }
  return {
    getSum: function () {
      return getX() + getY();
    }
  };
}

var classic_object = new ClassicObject();
var closure_object = new ClosureObject();

for (var i = 0; i < 1e5; i++) classic_object.getSum();
for (var i = 0; i < 1e5; i++) closure_object.getSum();

assembly
;;; @11: gap.
mov eax,[ebp+0x8]
;;; @12: check-non-smi.
test eax,0x1
jz 0x2b20a00a
;;; @14: check-maps.
cmp [eax-1],0x5380ed01
jnz 0x2b20a014
;;; @16: check-prototype-maps.
mov ecx,[0x5400a694]
cmp [ecx-1],0x5380ece1
jnz 0x2b20a01e
;;; @18: load-named-field.
mov ecx,[eax+0xb]
;;; @24: load-named-field.
mov edx,[eax+0xf]

assembly
;;; @12: load-context-slot.
mov ecx,[eax+0x1f]     ;; getX 로드
;;; @14: global-object.
mov edx,[eax+0x13]
;;; @16: global-receiver.
mov edx,[edx+0x13]
;;; @18: check-function.
cmp ecx,[0x5400a714]
jnz 0x2b20a00a
;;; @20: constant-t.
mov ecx,[0x5400a71c]
;;; @22: load-context-slot.
mov edx,[ecx+0x17]     ;; x 로드
;;; @28: load-context-slot.
mov eax,[eax+0x23]     ;; getY
;;; @30: check-function.
cmp eax,[0x5400a724]
jnz 0x2b20a014
;;; @32: constant-t.
mov ecx,[0x5400a72c]
;;; @34: load-context-slot.
mov eax,[ecx+0x1b]     ;; y 로드

javascript
var classic_objects = [new ClassicObject(), new ClassicObject()];
var closure_objects = [new ClosureObject(), new ClosureObject()];

for (var i = 0; i < 1e5; i++) classic_objects[i % 2].getSum();
for (var i = 0; i < 1e5; i++) closure_objects[i % 2].getSum();