Series Article Directory
| content | Reference link |
|---|---|
| Basic use of Vue | The basic use of Vue (one article to master the most basic knowledge points of Vue) |
| Vue communication and advanced features | Communication between Vue components and advanced features (communication between various components, custom v-model, nextTick, slots) |
| Vue advanced features | Advanced features of Vue (dynamic components, asynchronous loading, keep-alive, mixin, Vuex, Vue-Router) |
| Vue Principle 1 | Vue principle (understanding MVVM model, in-depth / monitoring data changes, monitoring array changes, in-depth understanding of virtual DOM) |
| Vue Principle 2 | Vue principle (diff algorithm, template compilation, component rendering and updating, JS implementation routing) |
| Vue Interview Questions | Web front-end interview high-frequency test site - Vue interview questions |
Article directory
1. Vue principle
1. Understand the MVVM model
componentized
- Componentization is to split a page into small functional modules
- Each functional module belongs to its own part of the independent function
- Makes the management and maintenance of the entire page very easy.
- asp jsp php is already componentized
- There is also a similar componentization in nodejs
data-driven view
- Traditional components are only statically rendered, and updates also depend on operating the DOM
- Data Driven Views - Vue MVVM
- Data Driven Views - React setState
MVVM model
2. The core API for monitoring data changes
- Once the data of the component data changes, the update of the view is triggered immediately
- The first step in implementing a data-driven view
- Core API - Object.defineProperty
- Due to some disadvantages of Object.defineProperty, Vue3.0 uses Proxy
- But Proxy is not compatible and cannot be polyfilled
Object.defineProperty() basic usage
Example: Basic Usage
const data = {
}
const name = 'zhangsan'
Object.defineProperty(data, "name", {
get: function () {
console.log('get')
},
set: function (newVal) {
console.log('set')
name = newVal
}
})
console.log(data.name) // get zhangsan
data.name = 'lisi' // set
3. How does vue deeply monitor data changes
Object.defineProperty Disadvantages
- Deep monitoring requires recursion to the end, and a large amount of calculation at one time
- Unable to monitor new/deleted properties (Vue.set, Vue.delete)
Example: The view is updated three times, and the new and deleted properties cannot be monitored
// 触发更新视图
function updateView() {
console.log('视图更新');
}
// 重新定义属性，监听起来
function defineReactive(target, key, value) {
// 深度监听
observer(value)
// 核心 API
Object.defineProperty(target, key, {
get() {
return value
},
set(newValue) {
if(newValue !== value) {
// 深度监听
observer(value)
// 设置新值
// 注意，value 一直在闭包中，此处设置完之后，再 get 时也是会获取最新的值
value = newValue
// 触发更新视图
updateView()
}
}
})
}
// 监听对象属性
function observer(target) {
if (typeof target !== 'object' || target === null) {
// 不是对象或数组
return target
}
// 重新定义各个属性（for in 也可以遍历数组）
for (let key in target) {
defineReactive(target, key, target[key])
}
}
// 准备数据
const data = {
name: 'zhangsan',
age: 20,
info: {
address: '北京' // 需要深度监听
}
}
// 监听数据
observer(data)
// 测试
data.name = 'lisi'
data.age = 21
// console.log('age', data.age)
data.x = '100' // 新增属性，监听不到 —— 所以有 Vue.set
delete data.name // 删除属性，监听不到 —— 所以有 Vue.delete
data.info.address = '上海' // 深度监听
// data.nums.push(4) // 监听数组
4. How does vue monitor array changes
Object.defineProperty Disadvantages
- Deep monitoring requires recursion to the end, and a large amount of calculation at one time
- Unable to monitor new/deleted properties (Vue.set, Vue.delete)
- Unable to natively monitor arrays, special handling is required
Example:
// 触发更新视图
function updateView() {
console.log('视图更新');
}
// 重新定义数组原型
const oldArrayProperty = Array.prototype
// 创建新对象，原型指向 oldArrayProperty，再扩展新的方法不会影响原型
const arrProto = Object.create(oldArrayProperty);
['push', 'pop', 'shift', 'unshift', 'splice'].forEach(methodName => {
arrProto[methodName] = function () {
updateView() // 触发视图更新
oldArrayProperty[methodName].call(this, ...arguments)
// 相当于 Array.prototype.push.call(this, ...arguments)
}
})
// 重新定义属性，监听起来
function defineReactive(target, key, value) {
// 深度监听
observer(value)
// 核心 API
Object.defineProperty(target, key, {
get() {
return value
},
set(newValue) {
if(newValue !== value) {
// 深度监听
observer(value)
// 设置新值
// 注意，value 一直在闭包中，此处设置完之后，再 get 时也是会获取最新的值
value = newValue
// 触发更新视图
updateView()
}
}
})
}
// 监听对象属性
function observer(target) {
if (typeof target !== 'object' || target === null) {
// 不是对象或数组
return target
}
// 如果是数组，就把 arrProto 赋值给数组的原型
if (Array.isArray(target)) {
target.__proto__ = arrProto
}
// 重新定义各个属性（for in 也可以遍历数组）
for (let key in target) {
defineReactive(target, key, target[key])
}
}
// 准备数据
const data = {
name: 'zhangsan',
age: 20,
info: {
address: '北京' // 需要深度监听
},
nums: [10, 20, 30]
}
// 监听数据
observer(data)
// 测试 - 监听数组
data.nums.push(4) // 监听数组
5. Virtual DOM
- vdom is an important cornerstone for implementing vue and react
- The diff algorithm is the core and most critical part of vdom
- DOM manipulation is very performance-intensive
- Before using jQuery, you can control the timing of DOM operations by yourself and manually adjust
- Vue and React are data-driven views, using VDOM
(1) Solution: VDOM
- With a certain complexity, it is difficult to reduce the number of calculations
- Can the calculation, more transferred to JS calculation? Because JS executes very fast
- vdom - Simulate DOM structure with JS, calculate minimal changes, manipulate DOM
(2) Simulate DOM structure with JS
Example: JS simulates DOM structure
HTML code
<div id="div1" class="container">
<p>vdom</p>
<ul style="font-size: 20px">
<li>a</li>
</ul>
</div>
JS code
{
tag: 'div',
props: {
className: 'container',
id: 'div1'
}
children: [
{
tag: 'p',
children: 'vdom'
},
{
tag: 'ul',
props: {
style: 'font-size: 20px'}
children: [
{
tag: 'li',
children: 'a'
}
]
}
]
}
(3) Learning vdom through snabbdom
- Simple and powerful vdom library, easy to learn and use
- Vue refers to its implementation of vdom and diff
- snabbdom reference link
Example:
<div id="container"></div>
<button id="btn-change">change</button>
<script src="https://cdn.bootcss.com/snabbdom/0.7.3/snabbdom.js"></script>
<script src="https://cdn.bootcss.com/snabbdom/0.7.3/snabbdom-class.js"></script>
<script src="https://cdn.bootcss.com/snabbdom/0.7.3/snabbdom-props.js"></script>
<script src="https://cdn.bootcss.com/snabbdom/0.7.3/snabbdom-style.js"></script>
<script src="https://cdn.bootcss.com/snabbdom/0.7.3/snabbdom-eventlisteners.js"></script>
const snabbdom = window.snabbdom
// 定义 patch
const patch = snabbdom.init([
snabbdom_class,
snabbdom_props,
snabbdom_style,
snabbdom_eventlisteners
])
// 定义 h
const h = snabbdom.h
const container = document.getElementById('container')
// 生成 vnode
const vnode = h('ul#list', {
}, [
h('li.item', {
}, 'Item 1'),
h('li.item', {
}, 'Item 2')
])
patch(container, vnode)
document.getElementById('btn-change').addEventListener('click', () => {
// 生成 newVnode
const newVnode = h('ul#list', {
}, [
h('li.item', {
}, 'Item 1'),
h('li.item', {
}, 'Item B'),
h('li.item', {
}, 'Item 3')
])
patch(vnode, newVnode)
// vnode = newVnode // patch 之后，应该用新的覆盖现有的 vnode ，否则每次 change 都是新旧对比
})
Before changing:
After changing:
(4) vdom summary
- Simulate DOM structure with JS (vnode)
- Compare the old and new vnodes, get the smallest update range, and finally update the DOM
- Effectively control DOM operations in a data-driven view mode
不积跬步无以至千里 不积小流无以成江海
Click to follow and don't get lost, continue to update...