1. What is a responsive system
In Vue, we can use the data attribute to define the data of the component. This data can be used in templates, and the relevant DOM elements are automatically updated when these data change. This process is the core of a responsive system. For example, we define a count property in the Vue component:
<template>
<div>{{ count }}</div>
</template>
<script>
export default {
data() {
return {
count: 0
}
}
}
</script>
When we update the value of count in the component, the relevant DOM elements will also be automatically updated:
+= 1
How is this process implemented? Next, let’s discuss the implementation principle of Vue responsive system.
II. Implementation principle
The implementation of Vue responsive system is mainly implemented through the () method. This method can hijack the object's properties, so that some operations can be performed automatically when the object's properties change.
In Vue, each component instance has one$dataProperties, it is the data object of the component. Vue will use it()Method will$dataEach property in the object is converted togetter/setter. When we visit$dataWhen an attribute in an object, Vue will record the attributegetter, When this property changes, Vue will automatically call all the propertiesgetter, to update the relevant DOM elements.
For example, we can manually$dataA property in the object is converted togetter/setter：
let queue = []
function flushQueue() {
((watcher) => ())
queue = []
}
function queueWatcher(watcher) {
(watcher)
nextTick(flushQueue)
}
class Watcher {
constructor() {
queueWatcher(this)
}
run() {
('Update DOM elements')
}
}
const data = { count: 0 }
(data, 'count', {
get() {
('Get the value of count')
return value
},
set(newValue) {
('Set count value to', newValue)
value = newValue
new Watcher()
}
})
// Update count property = 1
= 2
When we update the count property, the set() method is triggered and a Watcher object is created. This Watcher object will be added to the queue. When all update operations are completed, Vue will call the run() method of all Watcher objects in the queue in turn to update the relevant DOM elements.
3. Virtual DOM implementation
In Vue, in addition to responsive systems, another very important concept is virtual DOM. A virtual DOM is a lightweight JavaScript object that corresponds to a real DOM element. Vue uses virtual DOM to improve performance and avoid frequent operation of real DOM elements.
Vue's virtual DOM implementation is mainly implemented through the diff algorithm. The diff algorithm can compare the differences between two trees and apply these differences to real DOM elements. For example, we can manually implement a simple diff algorithm:
Insert code slice herefunction diff(oldNode, newNode) {
if (!oldNode) {
return { type: 'add', node: newNode }
}
if (!newNode) {
return { type: 'remove', node: oldNode }
}
if ( !== ) {
return { type: 'replace', node: newNode }
}
if ( !== ) {
return { type: 'text', node: newNode }
}
const diffChildren = []
const oldChildren = || []
const newChildren = || []
const len = (, )
for (let i = 0; i < len; i++) {
const childDiff = diff(oldChildren[i], newChildren[i])
if (childDiff) {
(childDiff)
}
}
if () {
return { type: 'children', children: diffChildren }
}
}
const oldNode = {
type: 'div',
children: [
{
type: 'p',
text: 'Old child elements'
}
]
}
const newNode = {
type: 'div',
children: [
{
type: 'p',
text: 'New child elements'
}
]
}
const diffResult = diff(oldNode, newNode)
(diffResult)
When we compare two nodes, if the two nodes are the same, null is returned. If the two nodes are different, an object describing the difference in the node is returned. This object contains a type attribute that represents the type of node difference, and a node attribute that represents a new node.
For example, when we compare the two nodes above, an object describing the differences in the node will be returned:
{
type: 'children',
children: [
{
type: 'text',
node: {
type: 'p',
text: 'New child elements'
}
}
]
}
When we get the description object of node differences, we can apply these differences to the real DOM element, thereby updating the DOM element.
4. Summary
Vue is a very powerful and flexible front-end framework, with its responsive system and virtual DOM implementations being one of its core functions. This article discusses the principles and underlying implementation of Vue responsive systems and virtual DOM. I hope this article will be helpful for everyone to understand the principles of Vue.
This is the article about the detailed explanation of Vue responsive principles and virtual DOM implementation steps. For more related content on Vue responsive principles, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!