构造函数

function Person(name,age,job){
   this.name=name;
   this.age=age;
   this.job=job;
 }
var person=new Person(‘Tom‘,28,‘Teacher‘);
console.log(person.name);//Tom

 function Person(name,age,job){
   this.name=name;
   this.age=age;
   this.job=job;
 }
var person=Person(‘Tom‘,28,‘Teacher‘);
console.log(person);//undefined
console.log(window.name);//Tom

 function Person(name,age,job){
    if(this instanceof Person){
      this.name=name;
      this.age=age;
      this.job=job;
    }else{
      return new Person(name,age,job);
    }
 }
var person=Person(‘Tom‘,28,‘Teacher‘);
console.log(person.name); // Tom
var person=new Person(‘Tom‘,28,‘Teacher‘);
console.log(person.name); // Tom