React系列

React系列 — 简单模拟语法(一)
React系列 — Jsx, 合成事件与Refs(二)
React系列 — virtualdom diff算法实现分析(三)
React系列 — 从Mixin到HOC再到HOOKS(四)
React系列 — createElement, ReactElement与Component部分源码解析(五)
React系列 — 从使用React了解Css的各种使用方案(六)

前言

我们先不讲什么语法原理,先根据API效果强行模拟语法使用,实现一个简易版的React.

render

第一步我们先用类创建一个元素返回,并且绑定点击事件,代码如下,可以正常看到一个按钮出现了.

class AddButton {
  createDOM(domString) {
    const div = document.createElement("div");
    div.innerHTML = domString;
    return div;
  }

  render() {
    this.dom = this.createDOM(`<button>0</button>`);
    this.dom.addEventListener("click", () => console.log("click"), false);
    return this.dom;
  }
}

document.body.appendChild(new AddButton().render());

state && setState

实现类状态和修改状态方法

class AddButton {
  constructor() {
    this.state = { num: 0 };
  }

  createDOM(domString) {
    const div = document.createElement("div");
    div.innerHTML = domString;
    return div;
  }

  setState(state) {
    this.state = state;
    this.dom = this.render();
  }

  handleAdd() {
    const num = this.state.num + 1;
    this.setState({
      num: num
    });
  }

  render() {
    this.dom = this.createDOM(`<button id="btn">${this.state.num}</button>`);
    this.dom.addEventListener("click", () => this.handleAdd(), false);
    console.log(this.dom);
    return this.dom;
  }
}

document.body.appendChild(new AddButton().render());

渲染之后看到this dom输出已经发现改变了,但是视图并没有渲染,那是因为这是结尾一次性插入,下面就渲染视图这块往下走

重新渲染

我们现在把插入数据的操作内置到class里面,新增一个方法插入新元素移除旧元素.

class AddButton {
  constructor() {
    this.state = { num: 0 };
  }

  createDOM(domString) {
    const div = document.createElement("div");
    div.innerHTML = domString;
    return div;
  }

  changeDom() {
    const oDom = this.dom;
    this.dom = this.render();
    document.body.insertBefore(this.dom, oDom);
    document.body.removeChild(oDom);
  }

  setState(state) {
    this.state = state;
    this.changeDom();
  }

  handleAdd() {
    const num = this.state.num + 1;
    this.setState({
      num: num
    });
  }

  render() {
    this.dom = this.createDOM(`<button id="btn">${this.state.num}</button>`);
    this.dom.addEventListener("click", () => this.handleAdd(), false);
    return this.dom;
  }
}

document.body.appendChild(new AddButton().render());

现在效果虽然实现,但是还是得开头手动把元素插入视图

抽取公用类

我们先将一些共有方法提取到一个单独类

class Component {
  constructor() {}

  createDOM(domString) {
    const div = document.createElement("div");
    div.innerHTML = domString;
    return div;
  }

  changeDom() {
    const oDom = this.dom;
    this.dom = this._render();
    this.wrapper.insertBefore(this.dom, oDom);
    this.wrapper.removeChild(oDom);
  }

  setState(state) {
    this.state = state;
    this.changeDom();
  }

  _render(wrapper) {
    if (wrapper) this.wrapper = wrapper;
    this.dom = this.createDOM(this.render());
    this.dom.addEventListener("click", () => this.handleAdd(), false);
    return this.dom;
  }
}

然后组件只需要直接继承Component然后处理自己逻辑即可

class AddButton extends Component {
  constructor() {
    super();
    this.state = { num: 0 };
  }

  handleAdd() {
    const num = this.state.num + 1;
    this.setState({
      num: num
    });
  }

  render() {
    return `<button id="btn">${this.state.num}</button>`;
  }
}

还有一个问题是点击事件暂时还是耦合进Component里面,先略过不提.

ReactDom.render

大家都知道React会提供这么一个方法将组件插入一个指定元素,我们直接模拟

const ReactDom = {
  render(component, wrapper) {
    wrapper.appendChild(component._render(wrapper));
  }
};

ReactDom.render(new AddButton(), document.getElementById("root"));

Props

还有一个重要的传输数据实现如下

const ReactDom = {
  render(component, wrapper) {
    wrapper.appendChild(component._render(wrapper))
  }
}

class Component {
  constructor(props = {}) {
    this.props = props
  }

  createDOM(domString) {
    const div = document.createElement("div")
    div.innerHTML = domString
    return div
  }

  changeDom() {
    const oDom = this.dom
    this.dom = this._render()
    this.wrapper.insertBefore(this.dom, oDom)
    this.wrapper.removeChild(oDom)
  }

  setState(state) {
    this.state = state
    this.changeDom()
  }

  _render(wrapper) {
    if (wrapper) this.wrapper = wrapper
    this.dom = this.createDOM(this.render())
    this.dom.addEventListener("click", () => this.handleAdd(), false)
    return this.dom
  }
}

class AddButton extends Component {
  constructor(props) {
    super(props)
    this.state = { num: 0 }
  }

  handleAdd() {
    const num = this.state.num + 1
    this.setState({
      num: num
    })
  }

  render() {
    console.log(this.props)
    return `<button id="btn">${this.state.num}</button>`
  }
}

ReactDom.render(new AddButton({a:1}), document.getElementById("root"))

至此,抛开实际思路不说,我们已经简单模拟出来React的一般语法实现了.