命题点一：原型基础 + 构造函数基础
var A = function() {};
A.prototype.n = 1;
var b = new A();
A.prototype = {
n: 2,
m: 3
}
var c = new A();
console.log(b.n);
console.log(b.m);
console.log(c.n);
console.log(c.m);
// 1、undefined、2、3
命题点二：自有属性与原型继承属性
function A() {
this.name = 'a'
this.color = ['green', 'yellow']
}
function B() {}
B.prototype = new A()
var b1 = new B()
var b2 = new B()
b1.name = 'change'
b1.color.push('black')
console.log(b2.name) // 'a'
console.log(b2.color) // ["green", "yellow", "black"]
命题点三：构造函数综合考察
