Vue3之事件绑定的实现逻辑详解

let click = () => {
  console.log("点击我，很快乐")
};

<!-- template -->
<div v-on:click="click">点击我吧</div>

const _hoisted_1 = ["onClick"]

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

    return (_openBlock(), _createElementBlock("div", { onClick: click }, "点击我吧", 8 /* PROPS */, _hoisted_1))
  }
}

export const patchProp: DOMRendererOptions['patchProp'] = (
  el,
  key,
  prevValue,
  nextValue,
  isSVG = false,
  prevChildren,
  parentComponent,
  parentSuspense,
  unmountChildren
) => {
  if (isOn(key)) {
    patchEvent(el, key, prevValue, nextValue, parentComponent)
  }
}

function patchEvent(el, rawName, prevValue, nextValue, instance = null) {
  // vei = vue event invokers
  const invokers = el._vei || (el._vei = {});
  
  if (添加) {
    const invoker = (invokers[rawName] = createInvoker(nextValue, instance));
    el.addEventListener(event, handler, options)
  } else {
    el.removeEventListener(event, handler, options)
  }
}

export const withModifiers = (fn: Function, modifiers: string[]) => {
  return (event: Event, ...args: unknown[]) => {
    for (let i = 0; i < modifiers.length; i++) {
      const guard = modifierGuards[modifiers[i]]
      if (guard && guard(event, modifiers)) return
    }
    return fn(event, ...args)
  }
}

const modifierGuards: Record<
  string,
  (e: Event, modifiers: string[]) => void | boolean
> = {
  stop: e => e.stopPropagation(),
  prevent: e => e.preventDefault(),
  self: e => e.target !== e.currentTarget,
  ctrl: e => !(e as KeyedEvent).ctrlKey,
  shift: e => !(e as KeyedEvent).shiftKey,
  alt: e => !(e as KeyedEvent).altKey,
  meta: e => !(e as KeyedEvent).metaKey,
  left: e => 'button' in e && (e as MouseEvent).button !== 0,
  middle: e => 'button' in e && (e as MouseEvent).button !== 1,
  right: e => 'button' in e && (e as MouseEvent).button !== 2,
  exact: (e, modifiers) =>
    systemModifiers.some(m => (e as any)[`${m}Key`] && !modifiers.includes(m))
}

<Son v-on:children-clicked="childClickedHandler" />
<p>{{ date }}</p>

setup() {

  let childClickedHandler = (data: Date) => {
    date.value = data.getTime();
  }

  let date = ref(new Date().getTime());

  return {
    date,
    childClickedHandler
  };
},

<div v-on:click="clickevent">点击我吧</div>

emits: ["childrenClicked"],
setup(props, {emit}) {

  let clickevent = () => {
    emit('childrenClicked', new Date());
  }
  return {clickevent};
},            

_createVNode(_component_Son, { onChildrenClicked: childClickedHandler }, null, 8 /* PROPS */, ["onChildrenClicked"])

const _hoisted_1 = ["onClick"]

_createElementBlock("div", {
    onClick: $event => ($emit('childrenClicked', new Date()))
}, "点击我吧", 8 /* PROPS */, _hoisted_1)

export function createSetupContext(
  instance: ComponentInternalInstance
): SetupContext {
    return {
      get attrs() {
        return attrs || (attrs = createAttrsProxy(instance))
      },
      slots: instance.slots,
      emit: instance.emit,
      expose
    }
  }
}

export function emit(
  instance: ComponentInternalInstance,
  event: string,
  ...rawArgs: any[]
) {
  const props = instance.vnode.props || EMPTY_OBJ

  // 传入的传参
  let args = rawArgs
  
  // TODO: 处理v-mode的方法
  const isModelListener = event.startsWith('update:')

  // 处理函数名，on+首字母大写的函数名 或者 on+驼峰命名的函数名 
  let handlerName
  let handler =
    props[(handlerName = toHandlerKey(event))] ||
    props[(handlerName = toHandlerKey(camelize(event)))]
  if (!handler && isModelListener) {
    handler = props[(handlerName = toHandlerKey(hyphenate(event)))]
  }

  if (handler) {
    // 调用函数，参数是外部传入的参数
    callWithAsyncErrorHandling(
      handler,
      instance,
      ErrorCodes.COMPONENT_EVENT_HANDLER,
      args
    )
  }
  
}