JS Note 2: What does new do? How to implement new operation

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Js inheritance is always not understood, know the new operation after finally understand the point.Juejin. Cn/post / 684490… www.jianshu.com/p/66f3aef3e… Github.com/mqyqingfeng…

1. Why is new needed

When learning c++, we know that new is to save code to mass produce objects. After learning some js, we know that new can not only save code, but also save memory.

// constructorfunction Person(name, age, job) {
    this.name = name;
    this.age = age;
    this.job = job;
    this.friends = ["Shelby"."Court"]; } // Person. Prototype = {sayName:function() {
        returnthis.name; }} person1 = new person (); person1 = new person ();"Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");
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2. What did New do

Person1 example

1. Create (or construct) a brand new object.

person1 = {}
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2. The new object will be connected by the implementation [[prototype]].

person1.__proto__ = Person.prototype
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3. This new object is bound to the function call’s this.

Constructor.apply(person1, arguments);
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4. If the function returns no other object, the function call in the new expression automatically returns the new object

return person1
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3. How to implement a new operation

function objectFactory() {

    var obj = new Object(),

    Constructor = [].shift.call(arguments);

    obj.__proto__ = Constructor.prototype;

    var ret = Constructor.apply(obj, arguments);

    return typeof ret === 'object' ? ret : obj;

};
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Because maybe the constructor has a return value in it (returns an object)