1 function Stack() {
 2   this.dataStore = [];
 3   this.top = 0; //指向栈顶的位置
 4   this.push = push;
 5   this.pop = pop;
 6   this.peek = peek;
 7   this.clear = clear;
 8   this.length = length;
 9   
10   function push(element) {
11     this.dataStore[this.top++] = element; //先赋值后++
12   }
13   
14   function peek() {
15     return this.dataStore[this.top - 1];
16   }
17 
18   function pop() {
19     return this.dataStore[--this.top]; //先--运算
20   }
21 
22   function clear() {
23     this.top = 0;
24   }
25 
26   function length() {
27     return this.top;
28   }
29 }
30 
31 var s = new Stack(); 
32 s.push("David"); 
33 s.push("Raymond"); 
34 s.push("Bryan"); 
35 console.log(s);
36 console.log("length: " + s.length());