function Person(name ,age){
this.name = name;
this.age = age;//此时的this是window
}
var person = new Person(张三，18)//在此 this为person

常用于模块引用,即借用别人的函数完成自己的行为，前提是你的需求要完全涵盖别人已经做好的东西
如
function Person(name, age, sex){
	this.name = name;
	this.age = age;
	this.sex = sex;
}

function Student(name,age,sex,tel,grade){
	Person.call(this, name, age, sex);
	this.tel = tel;
	this.grade = grade;
}