原型链继承function People(){this.name people}function Man(){this.name man}Man.prototype
原型链继承
function People(){ this.name = 'people';}function Man(){ this.name = 'man';}Man.prototype = new People();为原型赋值的是父类的实例,而不是引用
原型链继承
function People(){ this.name = 'people';}function Man(){ this.name = 'man';}Man.prototype = new People();