No new build of JavaScript

Look at the first step of jquery source code, for the creation of jquery objects to see the foggy, pondering half a day finally a little feeling, in this record

The first way:

var A = function () {

return a.prototype.init ();

}

A.prototype = {

Init:function () {

This.age = 50;

Console.log (this);

return this;

},

age:100

}

Console.log (A () = = = new A ());

1. analysis of why the result is true

the a.prototype.init () function is called internally by A ()

The constructor is called inside New A (), and its constructor is function () {return a.prototype.init ();} , the a.prototype.init () function is also called

2. Analyze What the A.prototype.init () function returns

That depends on this , judging who this is, and we're going to parse it when the function is called, because it's called as a property of the prototype object, so this is the prototype object A.prototype

This way of creating, no matter how many times A () You call, they are all the same objects returned, so the modification of the B object affects the A object, see

var a = a ();

var B = A ();

Console.log (A.age);

Console.log (B.age);

B.age = 22;

Console.log (A.age);

Console.log (B.age);

So how to solve this problem, then the second way, it is the way jquery used

The second way

var A = function () {

Return new A.prototype.init();//①

}

A.prototype = {

Init:function () {

This.age = 50;

Console.log (this);

return this;

},

age:100

}

a.prototype.init.prototype = A.prototype;//②

var a = new A ();

var B = new A ();

Console.log (A===B);

Console.log (A.age);

Console.log (B.age);

B.age = 22;

Console.log (A.age);

Console.log (B.age);

Analysis of the ① and ②

① in new A.prototype.init () has done three things

Create an empty object var obj = {};

the Obj object property _proto_ points to the prototype of the function a.prototype.init;

Replace this of the A.prototype.init function with the obj object, in the call to the a.prototype.init function, A.prototype.init.call (obj), and returns the new object

Because the prototype of the object returned by ① is a.prototype.init.prototype, it has nothing to do with a.prototype, so that the newly returned object can inherit from the A.prototype , so ② let a.prototype.init.prototype point to a.prototype

Therefore, the second way is to create an instance, and ensure that their respective scopes are independent.

No new build of JavaScript