作用域链 Scope Chain

Object.prototype.x = 10;
 
var w = 20;
var y = 30;
 

//console.log(x); // 10
 
(function foo() {
  var w = 40;
  var x = 100;

  with ({z: 50}) {
    console.log(w, x, y , z); // 40, 10, 30, 50
  }

  console.log(this.x, this.w); // 10, 20

  console.log(window.w); // 20
 
})();

Object.prototype.x = 10;
 
var w = 20;
var y = 30;
 

//console.log(x); // 10
 
(function foo() {
  var w = 40;
  var x = 100;

  with ({z: 50}) {
    console.log(this.w, this.x, this.y , z); // 20, 10, 30, 50
  }

  console.log(x, w); // 100, 40

  console.log(window.w); // 20
 
})();

Object.prototype.x = 10;
 
var w = 20;
var y = 30;
 

//console.log(x); // 10
 
(function foo() {
  var w = 40;
  var x = 100;
  
  (function(){
   console.log(w, x, y); //40,100,30
})();

 
})();