Working principle and implementation method of Vue instruction

<div id='app'>
  <input type="text" v-model="inputValue" v-focus>
</div>
<script>
  Vue.directive('focus', {
    // Call bind() when binding an element for the first time {
      console.log('bind')
    },
    // When the bound element is inserted into the DOM...
    inserted: function (el) {
      console.log('inserted')
      el.focus()
    },
    // Call update() when the component VNode is updated {
      console.log('update')
    },
    // Call componentUpdated() after all VNode and its child VNodes of the component where the instruction is located are updated {
      console.log('componentUpdated')
    },
    // Called only once, unbind() is called when the instruction is unbound from the element {
      console.log('unbind')
    }
  })
  new Vue({
    data: {
      inputValue: ''
    }
  }).$mount('#app')
</script>

// src/core/vdom/patch.js
const hooks = ['create', 'activate', 'update', 'remove', 'destroy']
export function createPatchFunction (backend) {
  let i, j
  const cbs = {}

  const { modules, nodeOps } = backend
  for (i = 0; i < hooks.length; ++i) {
    cbs[hooks[i]] = []
    // modules correspond to modules in vue, including class, style, domListener, domProps, attrs, directive, ref, transition
    for (j = 0; j < modules.length; ++j) {
      if (isDef(modules[j][hooks[i]])) {
        // Finally convert hooks to {hookEvent: [cb1, cb2 ...], ...} form cbs[hooks[i]].push(modules[j][hooks[i]])
      }
    }
  }
  // ....
  return function patch (oldVnode, vnode, hydrating, removeOnly) {
    // ...
  }
}

{
  tag: 'input',
  parent: ASTElement,
  directives: [
    {
      arg: null, // parameter end: 56, // end character position of the instruction isDynamicArg: false, // dynamic parameter, v-xxx[dynamicParams]='xxx' form call modifiers: undefined, // instruction modifier name: "model",
      rawName: "v-model", // Instruction name start: 36, // Instruction start character position value: "inputValue" // Template },
    {
      arg: null,
      end: 67,
      isDynamicArg: false,
      modifiers: undefined,
      name: "focus",
      rawName: "v-focus",
      start: 57,
      value: ""
    }
  ],
  // ...
}

with (this) {
    return _c('div', {
        attrs: {
            "id": "app"
        }
    }, [_c('input', {
        directives: [{
            name: "model",
            rawName: "v-model",
            value: (inputValue),
            expression: "inputValue"
        }, {
            name: "focus",
            rawName: "v-focus"
        }],
        attrs: {
            "type": "text"
        },
        domProps: {
            "value": (inputValue) // Attributes added when processing v-model instructions},
        on: {
            "input": function($event) { // Custom event added when processing v-model directive if ($event.target.composing)
                    return;
                inputValue = $event.target.value
            }
        }
    })])
}

// src/core/vdom/patch.js
function createElm (
    vnode,
    insertedVnodeQueue,
    parentElm,
    refElm,
    nested,
    ownerArray,
    index
  ) {
    // ...
    // createComponent has a return value, which is the method for creating components. If there is no return value, continue with the following method if (createComponent(vnode, insertedVnodeQueue, parentElm, refElm)) {
      return
    }

    const data = vnode.data
    // ....
    if (isDef(data)) {
        // After the real node is created, update the node attributes, including the instruction // The instruction will call the bind method for the first time, and then initialize the subsequent hooks method of the instruction invokeCreateHooks(vnode, insertedVnodeQueue)
    }
    // From bottom to top, insert(parentElm, vnode.elm, refElm)
    // ...
  }

// src/core/vdom/modules/directives.js

// By default, all methods thrown are updateDirectives method export default {
  create: updateDirectives,
  update: updateDirectives,
  destroy: function unbindDirectives (vnode: VNodeWithData) {
    // When destroyed, vnode === emptyNode
    updateDirectives(vnode, emptyNode)
  }
}

function updateDirectives (oldVnode: VNodeWithData, vnode: VNodeWithData) {
  if (oldVnode.data.directives || vnode.data.directives) {
    _update(oldVnode, vnode)
  }
}

function _update (oldVnode, vnode) {
  const isCreate = oldVnode === emptyNode
  const isDestroy = vnode === emptyNode
  const oldDirs = normalizeDirectives(oldVnode.data.directives, oldVnode.context)
  const newDirs = normalizeDirectives(vnode.data.directives, vnode.context)
  // callback after insertion const dirsWithInsert = [
  // Callback after update is complete const dirsWithPostpatch = []

  let key, oldDir, dir
  for (key in newDirs) {
    oldDir = oldDirs[key]
    dir = newDirs[key]
    // New element instruction, will execute the inserted hook method once if (!oldDir) {
      // new directive, bind
      callHook(dir, 'bind', vnode, oldVnode)
      if (dir.def && dir.def.inserted) {
        dirsWithInsert.push(dir)
      }
    } else {
      // existing directive, update
      // If the element already exists, the componentUpdated hook method dir.oldValue = oldDir.value will be executed once
      dir.oldArg = oldDir.arg
      callHook(dir, 'update', vnode, oldVnode)
      if (dir.def && dir.def.componentUpdated) {
        dirsWithPostpatch.push(dir)
      }
    }
  }

  if (dirsWithInsert.length) {
    // The real DOM is inserted into the page, and this callback method will be called const callInsert = () => {
      for (let i = 0; i < dirsWithInsert.length; i++) {
        callHook(dirsWithInsert[i], 'inserted', vnode, oldVnode)
      }
    }
    // VNode merge insert hooks
    if (isCreated) {
      mergeVNodeHook(vnode, 'insert', callInsert)
    } else {
      callInsert()
    }
  }

  if (dirsWithPostpatch.length) {
    mergeVNodeHook(vnode, 'postpatch', () => {
      for (let i = 0; i < dirsWithPostpatch.length; i++) {
        callHook(dirsWithPostpatch[i], 'componentUpdated', vnode, oldVnode)
      }
    })
  }

  if (!isCreate) {
    for (key in oldDirs) {
      if (!newDirs[key]) {
        // no longer present, unbind
        callHook(oldDirs[key], 'unbind', oldVnode, oldVnode, isDestroy)
      }
    }
  }
}

// src/core/vdom/patch.js
function patchVnode (
    oldVnode,
    vnode,
    insertedVnodeQueue,
    ownerArray,
    index,
    removeOnly
  ) {
    // ...
    const oldCh = oldVnode.children
    const ch = vnode.children
    // Fully update node attributes if (isDef(data) && isPatchable(vnode)) {
      for (i = 0; i < cbs.update.length; ++i) cbs.update[i](oldVnode, vnode)
      if (isDef(i = data.hook) && isDef(i = i.update)) i(oldVnode, vnode)
    }
    // ...
    if (isDef(data)) {
    // Call postpatch hook if (isDef(i = data.hook) && isDef(i = i.postpatch)) i(oldVnode, vnode)
    }
  }