Implement a mini Vue

Posted by aron on Sun, 19 Dec 2021 23:49:06 +0100

mini-vue

Implement a simple Vue js. To understand the principle of Vue response, mom doesn't have to worry that I won't use Vue anymore!

The technology is not yet mature and only a small part of functions are realized-- 2020/08/27

Technical implementation reference Pull hook education "big front end high salary training camp" 3-day experience course

Full version of Vue responsive principle

Picture quoted from Meng Sixing - schematic Vue response principle

Beggar Mini Vue

Before implementing Mini Vue, first look at the description on the official website. On Vue's official website, Deep response principle In, it is explained as follows:

Each component instance corresponds to a watcher instance, which will record the "contacted" data property as a dependency during component rendering. Then, when the setter of the dependency is triggered, it will notify the watcher to re render its associated components.

start

For technical reasons, instead of Virtual DOM and render, choose to directly operate DOM

In short, mini vue creates Vue instances

Vue class is responsible for injecting the attributes in data into Vue instances and calling Observer class and Compiler class.
The Observer class is responsible for data hijacking and converts each data into a getter and setter. Its core principle is through object Defineproperty implementation.
The Compiler class is responsible for parsing instructions and interpolation expressions (Methods for updating views).
The Dep class is responsible for collecting dependencies and adding observer patterns. Notify all observers corresponding to data Watcher to update the view. When the Observer class converts each data into a getter and setter, it will create a Dep instance to collect dependencies and send notifications. Collect dependencies in getters in each data. Notify the dependency in the setter, that is, notify all Watcher instances of the new view.
The Watcher class is responsible for re rendering the associated view after data update.

Detailed comments have been added to the implementation code, which is non-toxic and harmless, and can be viewed at ease

Vue class

class Vue {
  constructor(options) {
    // 1. Save the data of options
    this.$options = options || {}
    this.$data = options.data || {}
    this.$el = typeof options.el === 'string' ? document.querySelector(options.el) : options.el
    // 2. To facilitate calling (vm.msg), convert the members in data into getter s and setter s and inject them into Vue instances
    this._proxyData(this.$data)
    // 3. Call the Observer class to listen for data changes
    new Observer(this.$data)
    // 4. Call compiler class to parse instructions and interpolation expressions
    new Compiler(this)
  }
  _proxyData(data) {
    Object.keys(data).forEach(key => {
      Object.defineProperty(this, key, {
        enumerable: true,
        configurable: true,
        get() {
          return data[key]
        },
        set(newValue) {
          if (newValue === data[key]) {
            return
          }
          data[key] = newValue
        }
      })
    })
  }
}
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Observer class

class Observer {
  constructor(data) {
    this.walk(data)
  }
  // Traverse the attributes in data($data) and convert the attributes into responsive data
  walk(data) {
    if (!data || typeof data !== 'object') {
      return
    }
    Object.keys(data).forEach((key) => {
      this.defineReactive(data, key, data[key])
    })
  }
  // Define responsive data
  defineReactive(obj, key, value) {
    const that = this
    // Responsible for collecting dependencies and sending notifications
    let dep = new Dep()
    // Use recursion to convert deep (internal) attributes into responsive data
    this.walk(value)
    Object.defineProperty(obj, key, {
      enumerable: true,
      configurable: true,
      get() {
        // Collection dependency
        Dep.target && dep.addSub(Dep.target)
        return value
      },
      set(newValue) {
        if (value === newValue) {
          return
        }
        value = newValue
        // If the newly set value is an object, it is also converted to responsive data
        that.walk(newValue)
        // Send notification
        dep.notify()
      }
    })
  }
}
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Compiler class

class Compiler {
  constructor(vm) {
    this.vm = vm
    this.el = vm.$el
    this.compiler(this.el)
  }

  // Compile templates to handle text nodes and element nodes
  compiler(el) {
    const childNodes = el.childNodes
    Array.from(childNodes).forEach(node => {
      // Processing text nodes
      if (this.isTextNode(node)) {
        this.compilerText(node)
      } else if (this.isElementNode(node)) {
        // Processing element nodes
        this.compilerElement(node)
      }

      // Judge whether the node node has child nodes. If so, recursively call compile
      if (node.childNodes.length) {
        this.compiler(node)
      }
    })
  }

  // Compile element nodes, process instructions
  compilerElement(node) {
    // Traverse all attribute nodes
    Array.from(node.attributes).forEach(attr => {
      // Determine whether v-start instruction
      let attrName = attr.name
      if (this.isDirective(attrName)) {
        // For more elegant handling of different methods, subtract v from the instruction-
        attrName = attrName.substr(2)
        const key = attr.value
        this.update(node, key, attrName)
      }
    })
  }

  // Method of executing corresponding instruction
  update(node, key, attrName) {
    let updateFn = this[attrName + 'Updater']
    // The corresponding method is executed only when there are instructions
    updateFn && updateFn.call(this, node, this.vm[key], key)
  }

  // Processing v-text instructions
  textUpdater(node, value, key) {
    node.textContent = value

    // Create a Watcher object to update the view when the data changes
    new Watcher(this.vm, key, (newValue) => {
      node.textContent = newValue
    })
  }

  // Processing v-model instructions
  modelUpdater(node, value, key) {
    node.value = value

    // Create a Watcher object to update the view when the data changes
    new Watcher(this.vm, key, (newValue) => {
      node.value = newValue
    })

    // Bidirectional binding
    node.addEventListener('input', () => {
      this.vm[key] = node.value
    })
  }

  // Compile text nodes and process interpolation expressions
  compilerText(node) {
    const reg = /\{\{(.+?)\}\}/
    let value = node.textContent
    if (reg.test(value)) {
      // Consider only one layer of objects, such as data MSG = 'hello world', nested objects are not considered. It is assumed that there is only one interpolation expression.
      const key = RegExp.$1.trim()
      node.textContent = value.replace(reg, this.vm[key])

      // Create a Watcher object to update the view when the data changes
      new Watcher(this.vm, key, (newValue) => {
        node.textContent = newValue
      })
    }
  }

  // Determine whether an element attribute belongs to an instruction
  isDirective(attrName) {
    return attrName.startsWith('v-')
  }

  // Judge whether a node belongs to a text node
  isTextNode(node) {
    return node.nodeType === 3
  }

  // Judge whether the node book belongs to the element node
  isElementNode(node) {
    return node.nodeType === 1
  }
}
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Dep class

class Dep {
  constructor() {
    this.subs = []
  }
  // Add observer
  addSub(sub) {
    if (sub && sub.update) {
      this.subs.push(sub)
    }
  }
  // Send notification
  notify() {
    this.subs.forEach(sub => {
      sub.update()
    })
  }
}
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Watcher class

class Watcher {
  constructor(vm, key, cb) {
    this.vm = vm

    // Attribute name in data
    this.key = key

    // The callback function updates the view
    this.cb = cb

    // Record the watcher object into the static attribute target of the Dep class
    Dep.target = this
    // Trigger the get method, and addSub will be called in the get method
    this.oldValue = vm[key]
    Dep.target = null
  }

  // Update the view when the data changes
  update() {
    const newValue = this.vm[this.key]
    // The data is returned directly without change
    if (this.oldValue === newValue) {
      return
    }
    // update the view
    this.cb(newValue)
  }

}
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