es6-class

问题 I know of the ES6 await feature and I’d like to use it in a function I created in a class. It works well, but when the function is a static function, it doesn’t. Is there any reason for that? Also, what will be the right way to be able to use await inside a static function? class MyClass { resolveAfter2Seconds() { return new Promise(resolve => { setTimeout(() => { resolve('resolved'); }, 2000); }); } static async asyncCall() { console.log('calling'); var result = await this

问题 I' m building a page loader with canvas, and using the es6 classes... ALthough at the moment I can't make it work properly.. one of the reason is that I can't find a way to clear the canvas in progression. This is my code so far : class Loader { constructor (width, height) { this.width = width this.height = height } _init() { this._createCanvas() this._bindEvents() } // create canvas _createCanvas () { this.canvas = document.createElement("canvas") document.body.appendChild(this.canvas) this

问题 I want to pass child class instance to super class using super's constructor but I'm get this error super(this); this is not allowed before superclass constructor invocation Why i'm getting this error , also how could I resolve this issue class Parent { constructor(child) { this.child = child; } //...somewhere in code //child.doSomething(); } class Child extends Parent { constructor() { super(this); // <==== the error here } doSomething = () => { //... } } 回答1: There's no need to pass this to

问题 In ES5 it was possible to create multiple constructors for a class while keeping common parts to both using prototypes, as shown below function Book() { //just creates an empty book. } function Book(title, length, author) { this.title = title; this.Length = length; this.author = author; } Book.prototype = { ISBN: "", Length: -1, genre: "", covering: "", author: "", currentPage: 0, title: "", flipTo: function FlipToAPage(pNum) { this.currentPage = pNum; }, turnPageForward: function turnForward

问题 In ES5 it was possible to create multiple constructors for a class while keeping common parts to both using prototypes, as shown below function Book() { //just creates an empty book. } function Book(title, length, author) { this.title = title; this.Length = length; this.author = author; } Book.prototype = { ISBN: "", Length: -1, genre: "", covering: "", author: "", currentPage: 0, title: "", flipTo: function FlipToAPage(pNum) { this.currentPage = pNum; }, turnPageForward: function turnForward

问题 In ES5 it was possible to create multiple constructors for a class while keeping common parts to both using prototypes, as shown below function Book() { //just creates an empty book. } function Book(title, length, author) { this.title = title; this.Length = length; this.author = author; } Book.prototype = { ISBN: "", Length: -1, genre: "", covering: "", author: "", currentPage: 0, title: "", flipTo: function FlipToAPage(pNum) { this.currentPage = pNum; }, turnPageForward: function turnForward

问题 In ES5 it was possible to create multiple constructors for a class while keeping common parts to both using prototypes, as shown below function Book() { //just creates an empty book. } function Book(title, length, author) { this.title = title; this.Length = length; this.author = author; } Book.prototype = { ISBN: "", Length: -1, genre: "", covering: "", author: "", currentPage: 0, title: "", flipTo: function FlipToAPage(pNum) { this.currentPage = pNum; }, turnPageForward: function turnForward

问题 In ES5 it was possible to create multiple constructors for a class while keeping common parts to both using prototypes, as shown below function Book() { //just creates an empty book. } function Book(title, length, author) { this.title = title; this.Length = length; this.author = author; } Book.prototype = { ISBN: "", Length: -1, genre: "", covering: "", author: "", currentPage: 0, title: "", flipTo: function FlipToAPage(pNum) { this.currentPage = pNum; }, turnPageForward: function turnForward

问题 In React quickstart, it is stated about Refs and Functional Components that You may not use the ref attribute on functional components because they don't have instances: function MyFunctionalComponent() { return <input />; } class Parent extends React.Component { render() { // This will *not* work! return ( <MyFunctionalComponent ref={(input) => { this.textInput = input; }} /> ); } } I don't fully understand the above statement and the example. So far from reading the tutorials, the only

问题 In React quickstart, it is stated about Refs and Functional Components that You may not use the ref attribute on functional components because they don't have instances: function MyFunctionalComponent() { return <input />; } class Parent extends React.Component { render() { // This will *not* work! return ( <MyFunctionalComponent ref={(input) => { this.textInput = input; }} /> ); } } I don't fully understand the above statement and the example. So far from reading the tutorials, the only