Those confusing concepts (3): function and class

ES6 Medium class class (oop Object-oriented programming ideas ) and function difference

The same thing ：

Can be used as a constructor , adopt new Operator to instantiate

Function implementation constructor

function Person(name) { 
    this.name = name 
} 
const user = new Person('Jack') 
console.log(user); // Person { name: 'Jack' }

Constructor class implementation , Among them constructor Method is a special method , Called constructor method ;

use new After creating the instance , Automatically call constructor, Does not define constructor, amount to constructor It's a null function

class Person { 
    constructor(name) { 
        this.name = name 
    } 
} 
const user = new Person('Jack')
console.log(user); // Person { name: 'Jack' } 

Difference

1、 Calling a class constructor must use new The operator , And ordinary. function Constructor if not used new, Will take the overall situation this, As internal objects

2、function Constructor declaration has variable promotion , You can use it first , class Declare that there is no variable promotion , The instantiated object must be written after the declaration

const user = new Person('jack') 

function Person(name) { 
    this.name = name 
}

3、class Not available call、apply、bind change this Point to