Detailed explanation of JavaScript constructors and prototypes with examples

This article brings you relevant knowledge aboutJavaScript, which mainly introduces related issues about constructors and prototypes, as well as prototype-related content. Let’s take a look at it together. I hope it will be helpful to everyone. helpful.

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1. Constructor and prototype

1.1 Use prototype to solve the problem of memory waste

Disadvantages: There is the problem of memory waste,

If there are two objects or more, the space of a complex data type will be opened multiple times

Constructor prototypeprototypeThe prototype object mainly solves the problem of memory waste. The function assigned by the constructor through the prototype is owned by all objectsshared. Every constructor in JavaScript has a prototype property that points to another object. This prototype is an object, and all properties and methods of the prototype object will be owned by the constructor. At this time, you can use prototype to put methods in it for use by all instance objects of the object.

Object prototype

_ proto_ObjectEvery object will have an attribute

_ proto_

Points to the prototype prototype object of the constructor. The reason why our object can use the properties and methods of the constructor prototype prototype object is because the object has_ proto_The existence of prototype.

sy's _ proto_ and sym's _ proto_ are the same method search rules: first look at sy, whether there is a sing method on the sym object, and if so, execute this Sing on the object, because there is _ _ proto _ _, go to the constructor function prototype object Prototype, and go to the constructor function prototype object Prototype to find the sing method (Simply put, I use it if I have it. , if not, go to the prototype object and look for it

) When the function and object are created, a property will be automatically created, both of which point to the same empty object

1.2 constructor constructor constructor Constructor

Object prototype (_

proto

_) and constructor (prototype) prototype object have a property

constructorproperty, constructor We call it a constructor because itrefers back to the constructor itself.

Both of them have constructors. If the prototype is added in the form of an object, then the prototype pointer has changed and points to a new one. The prototype object of this new object does not point to the construor. You need to point it manually

2. Prototype chain

2.1 Member search rules in js

When accessing the properties (including methods) of an object, first check whether the object itself has the property. If not, search for its prototype (that is, the prototype prototype object pointed to by ._ proto _). If it doesn't exist yet, look for the prototype of the prototype object (the prototype object of Object). And so on until Object is found (null).

2.2 Prototype object this points to

1. In the constructor, this points to the object instance shanyu

2.3 Extending built-in objects

You can extend the original built-in objects with customized methods through prototype objects.

Arrays and string built-in objects cannot be prototyped Object overwriting operation Array.prototype = {} If this operation is performed, the original method will be overwritten. The only way is Array.prototype. method name = function(){}.

3.call function

Call this function and modify the this pointer when the function is running. There are three parameters:thisArgThe object pointed to by the current calling function thisarg1, arg2Other parameters passed

4. Inherit

through us When typing, you can see that this points to Son, that is, Son uses the uname and uage in the parent constructor

##4.1 Utilizing prototype object inheritance

There was no extends before es6, so you can use the combination of

constructor and model objectto perform inheritance operations

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