为什么要用框架
一直在用Vue，但是也没有想过框架的出现是为了解决什么痛点？
实现一个点赞功能
首先，实现一个简单的点赞功能，不考虑使用任何框架。
<body>
<div class='wrapper'>
<button class='like-btn'>
<span class='like-text'>点赞</span>
<span>👍</span>
</button>
</div>
<script>
// 实现一个简单的点赞按钮，点击按钮的同时按钮的文字会变换。demo1难以复用
const button = document.querySelector('.like-btn')
const buttonText = button.querySelector('.like-text')
let isLiked = false
button.addEventListener('click', () => {
isLiked = !isLiked
if (isLiked) {
buttonText.innerHTML = '取消'
} else {
buttonText.innerHTML = '点赞'
}
}, false)
</script>
</body>以上代码实现了点赞的功能，但是有一个问题——难以复用。
结构复用
经过改造，我们也仅仅只能复用html部分，并且没有添加事件
<body>
<div class='wrapper'></div>
<script>
// 仅仅可以复用html部分，没有添加事件
class LikeButton {
render(){
return `
<button id='like-btn'>
<span class='like-text'>赞</span>
<span>👍</span>
</button>
`
}
}
const wrapper = document.querySelector('.wrapper')
const likeButton1 = new LikeButton()
wrapper.innerHTML = likeButton1.render()
const likeButton2 = new LikeButton()
wrapper.innerHTML += likeButton2.render()
</script>
</body>添加事件
虽然添加了click事件，但是只能输出固定的click。我们需要点击按钮，改变文字
<body>
<div class='wrapper'></div>
<script>
// 添加了click事件，但是只能打印固定的click
// ::String => ::Document
const createDOMFromString = (domString) => {
const div = document.createElement('div')
div.innerHTML = domString
return div
}
class LikeButton {
render(){
this.el = createDOMFromString(`
<button class='like-button'>
<span class='like-text'>点赞</span>
<span>👍</span>
</button>
`)
this.el.addEventListener('click', () => console.log('click'), false)
return this.el
}
}
const wrapper = document.querySelector('.wrapper')
const likeButton1 = new LikeButton()
wrapper.appendChild(likeButton1.render())
const likeButton2 = new LikeButton()
wrapper.appendChild(likeButton2.render())
</script>
</body>修改文字
点击按钮，会修改文字，但是changeLikeText方法频繁的操作dom，影响性能
<body>
<div class='wrapper'></div>
<script>
// 点击按钮会执行changeLikeText方法，但是changeLikeText方法里面在不停的操作dom，影响性能
// ::String => ::Document
const createDOMFromString = (domString) => {
const div = document.createElement('div')
div.innerHTML = domString
return div
}
class LikeButton {
constructor () {
this.state = { isLiked: false }
}
changeLikeText () {
const likeText = this.el.querySelector('.like-text')
this.state.isLiked = !this.state.isLiked
likeText.innerHTML = this.state.isLiked ? '取消' : '点赞'
}
render(){
this.el = createDOMFromString(`
<button class='like-button'>
<span class='like-text'>点赞</span>
<span>👍</span>
</button>
`)
this.el.addEventListener('click', this.changeLikeText.bind(this), false)
return this.el
}
}
const wrapper = document.querySelector('.wrapper')
const likeButton1 = new LikeButton()
wrapper.appendChild(likeButton1.render())
const likeButton2 = new LikeButton()
wrapper.appendChild(likeButton2.render())
</script>
</body>性能优化
到这一步骤，基本已经大体形成，我们可以做更进一步的优化。
<body>
<div class='wrapper'></div>
<script>
// 点击按钮执行changeLikeText方法，该方法值会调用setState方法，setState方法会重新给satate赋值，并且修改虚拟html。最终只会操作一次dom
// ::String => ::Document
const createDOMFromString = (domString) => {
const div = document.createElement('div')
div.innerHTML = domString
return div
}
class LikeButton {
constructor () {
this.state = { isLiked: false }
}
setState (state) {
const oldEl = this.el
this.state = state
this.el = this.render()
if (this.onStateChange) this.onStateChange(oldEl, this.el)
}
changeLikeText () {
this.setState({
isLiked: !this.state.isLiked
})
}
render () {
this.el = createDOMFromString(`
<button class='like-btn'>
<span class='like-text'>${this.state.isLiked ? '取消' : '点赞'}</span>
<span>👍</span>
</button>
`)
this.el.addEventListener('click', this.changeLikeText.bind(this), false)
return this.el
}
}
const wrapper = document.querySelector('.wrapper')
const likeButton = new LikeButton()
wrapper.appendChild(likeButton.render()) // 第一次插入 DOM 元素
likeButton.onStateChange = (oldEl, newEl) => {
wrapper.insertBefore(newEl, oldEl) // 插入新的元素
wrapper.removeChild(oldEl) // 删除旧的元素
}
</script>
</body>进一步优化
setState和_renderDOM封装成Component类，便于其他组件使用
<body>
<div class='wrapper'></div>
<script>
// 把setState和_renderDOM方法进行抽离，修改dom的操作封装成方法
// ::String => ::Document
const createDOMFromString = (domString) => {
const div = document.createElement('div')
div.innerHTML = domString
return div
}
const mount = (component, wrapper) => {
wrapper.appendChild(component._renderDOM())
component.onStateChange = (oldEl, newEl) => {
wrapper.insertBefore(newEl, oldEl)
wrapper.removeChild(oldEl)
}
}
class Component {
setState (state) {
const oldEl = this.el
this.state = state
this._renderDOM()
if (this.onStateChange) this.onStateChange(oldEl, this.el)
}
_renderDOM () {
this.el = createDOMFromString(this.render())
if (this.onClick) {
this.el.addEventListener('click', this.onClick.bind(this), false)
}
return this.el
}
}
class LikeButton extends Component {
constructor () {
super()
this.state = { isLiked: false }
}
onClick () {
this.setState({
isLiked: !this.state.isLiked
})
}
render () {
return `
<button class='like-btn'>
<span class='like-text'>${this.state.isLiked ? '取消' : '点赞'}</span>
<span>👍</span>
</button>
`
}
}
const wrapper = document.querySelector('.wrapper')
mount(new LikeButton(), wrapper)
</script>
</body>自定义配置
组件可通过props传参来自定义配置
<body>
<div class='wrapper'></div>
<script>
// 组件可以自定义配置 通过props
// ::String => ::Document
const createDOMFromString = (domString) => {
const div = document.createElement('div')
div.innerHTML = domString
return div
}
const mount = (component, wrapper) => {
wrapper.appendChild(component._renderDOM())
component.onStateChange = (oldEl, newEl) => {
wrapper.insertBefore(newEl, oldEl)
wrapper.removeChild(oldEl)
}
}
class Component {
constructor (props = {}) {
this.props = props
}
setState (state) {
const oldEl = this.el
this.state = state
this._renderDOM()
if (this.onStateChange) this.onStateChange(oldEl, this.el)
}
_renderDOM () {
this.el = createDOMFromString(this.render())
if (this.onClick) {
this.el.addEventListener('click', this.onClick.bind(this), false)
}
return this.el
}
}
class LikeButton extends Component {
constructor (props) {
super(props)
this.state = { isLiked: false }
}
onClick () {
this.setState({
isLiked: !this.state.isLiked
})
}
render () {
return `
<button class='like-btn' style="background-color: ${this.props.bgColor}">
<span class='like-text'>
${this.state.isLiked ? '取消' : '点赞'}
</span>
<span>👍</span>
</button>
`
}
}
class RedBlueButton extends Component {
constructor (props) {
super(props)
this.state = {
color: 'red'
}
}
onClick () {
this.setState({
color: 'blue'
})
}
render () {
return `
<div style='color: ${this.state.color};'>${this.state.color}</div>
`
}
}
const wrapper = document.querySelector('.wrapper')
mount(new LikeButton({ bgColor: 'red' }), wrapper)
</script>
</body>这样子循序渐进的看下来，就能体会到一个框架的诞生的个中缘由——并不是平白无故做出来的，而是为了解决一些问题，然后一点一点的优化，最终诞生的。