作用域安全的构造函数

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 person1 = Person("Nicholas", 29, "Software Engineer");
console.log(window.name);
console.log(person1.name);

var person2 = new Person("Shelby", 34, "Ergonomist");
console.log(person2.name);

添加了判断是否调用构造函数来确保this不会被加到window对象上