在Vue中给通过this.$refs引用的自定义控件添加类型声明

原创

一介程序员

修改于 2022-02-28 18:19:32

2.8K0

修改于 2022-02-28 18:19:32

0x00 hello world

最近在一个新项目中，尝试了vue2+typescript的组合，又又又碰到一个问题：定义了一个自定义控件Foo.vue，在控件中定义一个方法Bar()，使用自定义控件的时候，添加ref='foo'并且希望通过使用this.$refs.foo.Bar()调用方法，当然是可以成功调用的，但是在TypeScript中，他会报错。

后来我折腾了好久，想出了一个不是那么优雅的方法：

这个样子，虽然不报错了，但是生生的把TypeScript写成了AnyScript，如果我修改了Bar的定义，比如添加了一个参数，这边就不会提示错误，告诉我缺一个参数，就失去了使用TypeScript的意义。

0x01 优雅的方式

我试过(this.$refs.foo as Foo).Bar();不行，试过(this.$refs.foo as typeof Foo).Bar();不行，鬼使神差的，我试了下(this.$refs.foo as InstanceType<typeof Foo>).Bar();，居然可以！就觉得很神奇！这什么意思呀。

0x02 原理？

为了搞明白这到底是什么意思，我研究了一下vue的类型定义文件

Vue.extend的定义如下：

  extend<Data, Methods, Computed, PropNames extends string = never>(options?: ThisTypedComponentOptionsWithArrayProps<V, Data, Methods, Computed, PropNames>): ExtendedVue<V, Data, Methods, Computed, Record<PropNames, any>>;
  extend<Data, Methods, Computed, Props>(options?: ThisTypedComponentOptionsWithRecordProps<V, Data, Methods, Computed, Props>): ExtendedVue<V, Data, Methods, Computed, Props>;
  extend<PropNames extends string = never>(definition: FunctionalComponentOptions<Record<PropNames, any>, PropNames[]>): ExtendedVue<V, {}, {}, {}, Record<PropNames, any>>;
  extend<Props>(definition: FunctionalComponentOptions<Props, RecordPropsDefinition<Props>>): ExtendedVue<V, {}, {}, {}, Props>;
  extend(options?: ComponentOptions<V>): ExtendedVue<V, {}, {}, {}, {}>;

返回的是一个ExtendedVue，他的定义如下：

export type ExtendedVue<Instance extends Vue, Data, Methods, Computed, Props> = VueConstructor<CombinedVueInstance<Instance, Data, Methods, Computed, Props> & Vue>;

返回的是一个VueConstructor，他的定义如下：

export interface VueConstructor<V extends Vue = Vue> {
  new <Data = object, Methods = object, Computed = object, PropNames extends string = never>(options?: ThisTypedComponentOptionsWithArrayProps<V, Data, Methods, Computed, PropNames>): CombinedVueInstance<V, Data, Methods, Computed, Record<PropNames, any>>;
  // ideally, the return type should just contain Props, not Record<keyof Props, any>. But TS requires to have Base constructors with the same return type.
  new <Data = object, Methods = object, Computed = object, Props = object>(options?: ThisTypedComponentOptionsWithRecordProps<V, Data, Methods, Computed, Props>): CombinedVueInstance<V, Data, Methods, Computed, Record<keyof Props, any>>;
  new (options?: ComponentOptions<V>): CombinedVueInstance<V, object, object, object, Record<keyof object, any>>;

  extend<Data, Methods, Computed, PropNames extends string = never>(options?: ThisTypedComponentOptionsWithArrayProps<V, Data, Methods, Computed, PropNames>): ExtendedVue<V, Data, Methods, Computed, Record<PropNames, any>>;
  extend<Data, Methods, Computed, Props>(options?: ThisTypedComponentOptionsWithRecordProps<V, Data, Methods, Computed, Props>): ExtendedVue<V, Data, Methods, Computed, Props>;
  extend<PropNames extends string = never>(definition: FunctionalComponentOptions<Record<PropNames, any>, PropNames[]>): ExtendedVue<V, {}, {}, {}, Record<PropNames, any>>;
  extend<Props>(definition: FunctionalComponentOptions<Props, RecordPropsDefinition<Props>>): ExtendedVue<V, {}, {}, {}, Props>;
  extend(options?: ComponentOptions<V>): ExtendedVue<V, {}, {}, {}, {}>;

  nextTick<T>(callback: (this: T) => void, context?: T): void;
  nextTick(): Promise<void>
  set<T>(object: object, key: string | number, value: T): T;
  set<T>(array: T[], key: number, value: T): T;
  delete(object: object, key: string | number): void;
  delete<T>(array: T[], key: number): void;

  directive(
    id: string,
    definition?: DirectiveOptions | DirectiveFunction
  ): DirectiveOptions;
  filter(id: string, definition?: Function): Function;

  component(id: string): VueConstructor;
  component<VC extends VueConstructor>(id: string, constructor: VC): VC;
  component<Data, Methods, Computed, Props>(id: string, definition: AsyncComponent<Data, Methods, Computed, Props>): ExtendedVue<V, Data, Methods, Computed, Props>;
  component<Data, Methods, Computed, PropNames extends string = never>(id: string, definition?: ThisTypedComponentOptionsWithArrayProps<V, Data, Methods, Computed, PropNames>): ExtendedVue<V, Data, Methods, Computed, Record<PropNames, any>>;
  component<Data, Methods, Computed, Props>(id: string, definition?: ThisTypedComponentOptionsWithRecordProps<V, Data, Methods, Computed, Props>): ExtendedVue<V, Data, Methods, Computed, Props>;
  component<PropNames extends string>(id: string, definition: FunctionalComponentOptions<Record<PropNames, any>, PropNames[]>): ExtendedVue<V, {}, {}, {}, Record<PropNames, any>>;
  component<Props>(id: string, definition: FunctionalComponentOptions<Props, RecordPropsDefinition<Props>>): ExtendedVue<V, {}, {}, {}, Props>;
  component(id: string, definition?: ComponentOptions<V>): ExtendedVue<V, {}, {}, {}, {}>;

  use<T>(plugin: PluginObject<T> | PluginFunction<T>, options?: T): VueConstructor<V>;
  use(plugin: PluginObject<any> | PluginFunction<any>, ...options: any[]): VueConstructor<V>;
  mixin(mixin: VueConstructor | ComponentOptions<Vue>): VueConstructor<V>;
  compile(template: string): {
    render(createElement: typeof Vue.prototype.$createElement): VNode;
    staticRenderFns: (() => VNode)[];
  };

  observable<T>(obj: T): T;

  util: {
    warn(msg: string, vm?: InstanceType<VueConstructor>): void;
  };

  config: VueConfiguration;
  version: string;
}

注意前面3行，那几个名字为new的函数：

  new <Data = object, Methods = object, Computed = object, PropNames extends string = never>(options?: ThisTypedComponentOptionsWithArrayProps<V, Data, Methods, Computed, PropNames>): CombinedVueInstance<V, Data, Methods, Computed, Record<PropNames, any>>;
  // ideally, the return type should just contain Props, not Record<keyof Props, any>. But TS requires to have Base constructors with the same return type.
  new <Data = object, Methods = object, Computed = object, Props = object>(options?: ThisTypedComponentOptionsWithRecordProps<V, Data, Methods, Computed, Props>): CombinedVueInstance<V, Data, Methods, Computed, Record<keyof Props, any>>;
  new (options?: ComponentOptions<V>): CombinedVueInstance<V, object, object, object, Record<keyof object, any>>;

也就是说new一个Vue实例的时候，返回的类型是CombinedVueInstance，这个类型的定义如下：

export type CombinedVueInstance<Instance extends Vue, Data, Methods, Computed, Props> =  Data & Methods & Computed & Props & Instance;

这个 CombinedVueInstance 的用处就是把组件定义的内容和Vue本身的内容组合到一起。

0x03 总结

总结下来就是：

在JavaScript中，一个东西（函数？类型？）的类型有两种，一种是他本来的类型，一种是实例化之后的实例类型，这两个类型有可能是不一样的；
Vue的类型和Vue实例化的后的类型不是同一个类型，Vue的类型是VueConstructor类型，实例化后的类型是CombinedVueInstance；
我需要的是一个实例化之后的类型，所以Foo是我导入的一个变量，通过type of Foo取得它的类型，但是，但是我需要的是它实例化后的类型，所以还需要通过InstanceType<typeof Foo>获取。