es6-class

问题 Let's say you're developing a polyfill and don't want to shim a class if it already exists in the browser. How can this be done in ES6? The following is not valid because exports is not a statement: if (typeof Foo === 'undefined') { export class Foo { ... } } If the condition above evaluates to false , the importing script should get the browser built-in. 回答1: export should be static. For conditional exports CommonJS modules and exports can be used. It should be handled with ES6 modules this

问题 I understand the concept of constructors in OOP languages like C++. However, I am not entirely sure when to use a constructor in REACT. I do understand that JavaScript is object oriented, but I am not sure what the constructor is actually 'constructing'. When rendering a child component, do you need a constructor in the child component? For example: class App extends React.Component { constructor(props) { super(props); this.state = { items: [], error: null } } render () { return ( <React

问题 Both ES6 class and prototype of function have a contructor , but I'm wondering are they the same? Let me give more explanations. So, I create a Cat function, for instance: const Cat = function (name) { this.name = name; }; The Cat has the following prototype: This constructor can be lost if I type smth. like Cat.prototype = {}; , but new Cat('Name'); will continue working. Ang we have the following syntax in ES6: class Dog { constructor(name) { this.name = name; } } The class also has

问题 I'm currently implementing the static land specification (an alternative of fantasy land). I want to not only use plain objects as types but also ES2015 classes with static methods. I've implemented these static methods as arrow functions in curried form instead of normal functions. However, this isn't possible with ES2015 classes: class List extends Array { static map = f => xs => xs.map(x => f(x)) static of = x => [x] } My map doesn't need its own this , because it is merely a curried

问题 How do I clone a Javascript class instance using ES6. I'm not interested in solutions based on jquery or $extend. I've seen quite old discussions of object cloning that suggest that the problem is quite complicated, but with ES6 a very simple solution presents itself - I will put it below and see if people think it is satisfactory. edit: it is being suggested that my question is a duplicate; I saw that answer but it is 7 years old and involves very complicated answers using pre-ES6 js. I'm

问题 In ECMAScript 6 the typeof of classes is, according to the specification, 'function' . However also according to the specification you are not allowed to call the object created via the class syntax as a normal function call. In other words, you must use the new keyword otherwise a TypeError is thrown. TypeError: Classes can’t be function-called So without using try catch, which would be very ugly and destroy performance, how can you check to see if a function came from the class syntax or

问题 So I started converting my application from ES2015 to ES6 which uses React. I have a parent class and a child class like so, export default class Parent extends Component { constructor(props) { super(props); this.state = { code: '' }; } setCodeChange(newCode) { this.setState({code: newCode}); } login() { if (this.state.code == "") { // Some functionality } } render() { return ( <div> <Child onCodeChange={this.setCodeChange} onLogin={this.login} /> </div> ); } } Child class, export default

问题 So I started converting my application from ES2015 to ES6 which uses React. I have a parent class and a child class like so, export default class Parent extends Component { constructor(props) { super(props); this.state = { code: '' }; } setCodeChange(newCode) { this.setState({code: newCode}); } login() { if (this.state.code == "") { // Some functionality } } render() { return ( <div> <Child onCodeChange={this.setCodeChange} onLogin={this.login} /> </div> ); } } Child class, export default

问题 i'm struggling in what would be a good practice or better approach to communicate 'sibling classes in es6' quoted because they haven't a real parent class, by definition. let me explain better: class Car { constructor(typeOfMotor){ this.motor = typeOfMotor; this.mount(); this.addListener(); } mount() { // Some async logic here, and this will return true or false; } addListener(driver) { // Here i want to listen this.mount method and, // when return true, then call the ride method in the

问题 I am wondering how to access the native sessionStorage scope from within my custom methods. My example: https://jsfiddle.net/3mc7ao7j/1/ At line 3 I would like to be able to proxy through to my native sessionStorage after perform my mutation on the data. How do I access that scope again though? I know I can just call: sessionStorage.setItem() But that simply works because it is globally available and it feels wrong to do that. Mainly because I would also want to know how to do this without an