A brief discussion on the principle of new operator in JS

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new in javascript is a syntactic sugar. For those who have studied object-oriented languages ​​such as c++, java and c#, they think that in js There is a difference between classes and objects. In terms of implementation, js does not have classes. Everything is an object. It is more thorough than java.

The process of new is actually to create a new object and set the prototype of the new object to the constructor The prototype of the constructor function. In the process of using new, a total of three objects participate in the collaboration. The constructor function is the first object, the prototype object is two, and a newly generated empty object is the third object. Finally, it returns is an empty object, but this empty object is not vacuum, but already contains a prototype reference (proto)

The steps are as follows ：

(1) Create an empty object obj

(2) Let the proto member of the empty object (IE does not have this attribute) point to the constructor prototype member object

(3) Use apply to call the constructor function, and this is bound to the empty object obj.

(4) Return the empty object obj

#It is also possible to write a function yourself instead of using new. The sample code is as follows:

function NEW_OBJECT(Foo){

var obj={};
obj.proto=Foo.prototype;
obj.proto.constructor=Foo;
Foo.apply(obj,arguments)
return obj;

}

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