官术网_书友最值得收藏!

Writing a class-based component

In ECMAScript 6 (ES6), we got our first taste of real object-oriented programming in JavaScript with Classes. A class is declared in a fundamentally different way than our functional components, but most of the core tenets remain the same and there's not a huge amount more we need to learn to start using them.

The first thing we'll need to do is make a small modification to the import statement in src/Todo.js. We'll need to import not just React itself: we'll also need to import a particular named export specified in React, something called Component. Let's take a look at what the new import statement looks like:

import React, { Component } from 'react';

We have our Component imported as well, so let's explore the syntax for declaring a class:

class Todo extends Component { /* ... */ }

This tells JavaScript that we're building a new Todo class that inherits the functionality of Component (thus the extends keyword). Next, any React component we build as an ES6 class needs to have a render() function declared. To declare a function inside of a class, you just write the name, the arguments, and then the body inside of your class definition:

functionName(argument1, argument2) { /* ... */ }

React specifically requires us to declare a render() function with no arguments, as we mentioned earlier. Our return statement is identical to what we had in our previous functional component, so putting everything together we should end up with something similar to this:

class Todo extends Component {
render() {
return <div className="Todo">{this.props.description}</div>;
}
}

Here, we write out our render() { … } function, which is largely unchanged except for one small change: props.description is now this.props.description!

The reason for this is that props is not something that is just an argument on a function anymore. It's actually part of a class-specific property, so we need to tell JavaScript that when we say props, we actually mean the props local to this class. We just shorthand that with this.props! With that out of the way, we can start diving even further into the world of state!

主站蜘蛛池模板: 黄梅县| 丹凤县| 泽库县| 扶余县| 乌兰浩特市| 抚松县| 玛纳斯县| 宁河县| 融水| 南雄市| 民权县| 五家渠市| 邵阳县| 浮山县| 宁乡县| 崇礼县| SHOW| 德钦县| 界首市| 布拖县| 晋州市| 莱西市| 会泽县| 高平市| 上栗县| 南召县| 乐昌市| 瑞金市| 康马县| 镇巴县| 弥勒县| 宿迁市| 广昌县| 登封市| 伊川县| 长泰县| 淄博市| 含山县| 天祝| 汉中市| 封开县|