As a front end, you need to know how JavaScript implements inheritance

Tell me Zhan to hide 2020-11-06 20:48:33
end know javascript implements inheritance


stay ES6 Before ,javascript Not like any other language , There are ways to inherit directly , It needs the help of constructors + Prototype object simulation implementation inheritance . Now we can use it ES6 Of extends Method to implement inheritance , If you want to know more about ES6 See the implemented inheritance 《ES6 Learning notes ( Two ): Teach you how to play with class inheritance and class objects 》, No more introduction here .

ES6 We have not been provided with extends Inherit , We can use constructors + Prototype object simulation implementation inheritance , It's called combinatorial inheritance .

1. call()

Call this function , And modify the function runtime this Point to

fun.call(thisArg, arg1,arg2,...)
  • thisArg: The current call function this Point to object of
  • arg1, arg2: Common parameters passed
function fn() {

console.log(' Front end Lanfeng ')
console.log(this)
}
fn.call() // explain call() You can call functions ,this Point to window
var obj = {

name: 'lanfeng
}
fn.call(obj) //this Point to obj, explain call You can change this Point to 

2. Borrow constructor to inherit parent type properties

The core idea : adopt call() Put the parent type of this Pointing to a subtype this, In this way, the child type can inherit the properties of the parent type .

// Inheriting properties from a parent constructor 
// Parent constructor 
function Father (uname, age) {

//this Object instance pointing to the parent constructor 
this.uname = uname
this.age = age
}
// Child constructors 
function Son (uname, age){

// this Object instance pointing to the child constructor 
// With the help of call,this Point to the child constructor object instance 
Father.call(this, uname, age)
}
var son = new Son(' Juen-Kai Wang ',18)
console.log(son) //

3. Inheriting parent type methods from prototype objects

// Parent constructor 
function Father (uname, age) {

//this Object instance pointing to the parent constructor 
this.uname = uname
this.age = age
}
// The parent prototype method 
Father.prototype.money = function() {

console.log(10000)
}
// Child constructors 
function Son (uname, age){

// this Object instance pointing to the child constructor 
// With the help of call,this Point to the child constructor object instance 
Father.call(this, uname, age)
}
// Son.prototype = Father.prototype There will be problems with direct assignment , If you modify the child prototype object , The parent prototype object also changes /
Son.prototype = new Father()
// Manual modification constructor Point back to the original constructor 
Son.prototype.constructor = Son
Son.prototype.exam= function() {

console.log(' The test ')
}
var son = new Son(' Juen-Kai Wang ',18)
console.log(son) //
son

The structural relationship is shown in the figure below :
image.png

summary

Today I mainly share call() Methods and javascript By constructor + Prototype objects simulate the way inheritance is implemented .

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