一篇文章告诉你Vue3指令是如何实现的

app.directive('pin', (el, binding) => {
  el.style.position = 'fixed'
  const s = binding.arg || 'top'
  el.style[s] = binding.value + 'px'
})

<!-- apiCreateApp.js -->
directive(name: string, directive?: Directive) {
  
  // 挂载在全局的`context`的`directives`对象上
  context.directives[name] = directive
  
  return app
},

directives: {
  pin: (el, binding) => {
    el.style.position = 'fixed'
    const s = binding.arg || 'top'
    el.style[s] = binding.value + 'px'
  }
}

<!-- component.ts -->
export function applyOptions(instance: ComponentInternalInstance) {
  
  // 挂载在组件实例对象的`directives`上    
  instance.directives = directives
  
}

function render(_ctx, _cache) {
  with (_ctx) {
    const { openBlock: _openBlock, createElementBlock: _createElementBlock } = _Vue

    return (_openBlock(), _createElementBlock("h4", null, "指令演示"))
  }
}

function render(_ctx, _cache) {
  with (_ctx) {
    const { createTextVNode: _createTextVNode, resolveDirective: _resolveDirective, withDirectives: _withDirectives, openBlock: _openBlock, createElementBlock: _createElementBlock } = _Vue

    const _directive_pin = _resolveDirective("pin")

    return _withDirectives((_openBlock(), _createElementBlock("h4", null, _hoisted_2, 512 /* NEED_PATCH */)), [
      [_directive_pin, pinPadding, direction]
    ])
  }
}

export function resolveDirective(name: string): Directive | undefined {
  return resolveAsset(DIRECTIVES, name)
}

function resolveAsset(
  type: AssetTypes,
  name: string,
  warnMissing = true,
  maybeSelfReference = false
) {
    const res =
    // local registration
    // check instance[type] first which is resolved for options API
    resolve(instance[type] || (Component as ComponentOptions)[type], name) ||
    // global registration
    resolve(instance.appContext[type], name)

    return res
}

export function withDirectives<T extends VNode>(
  vnode: T,
  directives: DirectiveArguments
): T {
    
  const bindings: DirectiveBinding[] = vnode.dirs || (vnode.dirs = [])
  
  for (let i = 0; i < directives.length; i++) {
    let [dir, value, arg, modifiers = EMPTY_OBJ] = directives[i]
    if (isFunction(dir)) {
      dir = {
        mounted: dir,
        updated: dir
      } as ObjectDirective
    }
    bindings.push({
      dir,
      instance,
      value,
      oldValue: void 0,
      arg,
      modifiers
    })
  }
  return vnode
}

const mountElement = (
  vnode: VNode,
  container: RendererElement,
  anchor: RendererNode | null,
  parentComponent: ComponentInternalInstance | null,
  parentSuspense: SuspenseBoundary | null,
  isSVG: boolean,
  slotScopeIds: string[] | null,
  optimized: boolean
) => {
    // 1
    if (dirs) {
      invokeDirectiveHook(vnode, null, parentComponent, 'created')
    }
    // 2
    if (dirs) {
        invokeDirectiveHook(vnode, null, parentComponent, 'beforeMount')
    }
    
    // 3
    queuePostRenderEffect(() => {
      vnodeHook && invokeVNodeHook(vnodeHook, parentComponent, vnode)
      needCallTransitionHooks && transition!.enter(el)
      dirs && invokeDirectiveHook(vnode, null, parentComponent, 'mounted')
    }, parentSuspense)
}

const patchElement = (
  n1: VNode,
  n2: VNode,
  parentComponent: ComponentInternalInstance | null,
  parentSuspense: SuspenseBoundary | null,
  isSVG: boolean,
  slotScopeIds: string[] | null,
  optimized: boolean
) => {
  const el = (n2.el = n1.el!)
  
  // 1
  if (dirs) {
    invokeDirectiveHook(n2, n1, parentComponent, 'beforeUpdate')
  }

  // 2
  queuePostRenderEffect(() => {
      vnodeHook && invokeVNodeHook(vnodeHook, parentComponent, n2, n1)
      dirs && invokeDirectiveHook(n2, n1, parentComponent, 'updated')
    }, parentSuspense)
}

const unmount: UnmountFn = (
  vnode,
  parentComponent,
  parentSuspense,
  doRemove = false,
  optimized = false
) => {
  const {
    type,
    props,
    ref,
    children,
    dynamicChildren,
    shapeFlag,
    patchFlag,
    dirs
  } = vnode
  // unset ref
  if (ref != null) {
    setRef(ref, null, parentSuspense, vnode, true)
  }

  if (shapeFlag & ShapeFlags.COMPONENT_SHOULD_KEEP_ALIVE) {
    ;(parentComponent!.ctx as KeepAliveContext).deactivate(vnode)
    return
  }

  const shouldInvokeDirs = shapeFlag & ShapeFlags.ELEMENT && dirs

  let vnodeHook: VNodeHook | undefined | null
  if ((vnodeHook = props && props.onVnodeBeforeUnmount)) {
    invokeVNodeHook(vnodeHook, parentComponent, vnode)
  }

  if (shapeFlag & ShapeFlags.COMPONENT) {
    unmountComponent(vnode.component!, parentSuspense, doRemove)
  } else {


    if (shouldInvokeDirs) {
      invokeDirectiveHook(vnode, null, parentComponent, 'beforeUnmount')
    }

    queuePostRenderEffect(() => {
      vnodeHook && invokeVNodeHook(vnodeHook, parentComponent, vnode)
      shouldInvokeDirs &&
        invokeDirectiveHook(vnode, null, parentComponent, 'unmounted')
    }, parentSuspense)
}

export function renderComponentRoot(
  instance: ComponentInternalInstance
): VNode {
  const {
    type: Component,
    vnode,
    proxy,
    withProxy,
    props,
    propsOptions: [propsOptions],
    slots,
    attrs,
    emit,
    render,
    renderCache,
    data,
    setupState,
    ctx,
    inheritAttrs
  } = instance

    // inherit directives
    if (vnode.dirs) {
      if (__DEV__ && !isElementRoot(root)) {
        warn(
          `Runtime directive used on component with non-element root node. ` +
            `The directives will not function as intended.`
        )
      }
      root.dirs = root.dirs ? root.dirs.concat(vnode.dirs) : vnode.dirs
    }
}