使用 JavaScript Class Mixins 与 TypeScript 声明文件

Question

我需要帮助在声明文件中使用 class mixins。 具体来说，当在 mixin 中定义方法时，typescript 不会在混合的 class 主体中提取它：

就我而言，我正在应用两个 mixin。 第一个 mixin - NotifyingElementMixin - 提供了一个名为notify的方法，正是这种方法无法应用于混合 class 主体

通知元素mixin.js

export const NotifyingElementMixin = superclass =>
  class NotifyingElement extends superclass {
    /**
     * Fires a `*-changed` event.
     *
     * @param  {string}     propName Name of the property.
     * @param  {any} value  property value
     * @protected
     */
    notify(propName, value) {
      this.dispatchEvent(
        new CustomEvent(`${propName}-changed`, {
          detail: { value },
        })
      );
    }
  };
};

通知元素mixin.d.ts

export declare class NotifyingElement {
  public notify(propName: string, value: any): void
}

export function NotifyingElementMixin<TBase extends typeof HTMLElement>
(superclass: TBase): TBase & NotifyingElement;

第二个mixin提供了其他属性和方法，但是为了这个问题，我简化了实现

阿波罗查询mixin.js

export const ApolloQueryMixin = 
  superclass => class extends superclass {
    data = null;
    is = 'Query';
  };

阿波罗查询mixin.d.ts

export declare class ApolloQuery<TCacheShape, TData, TVariables, TSubscriptionData = TData> {
  data: null
  is: string
}

type Constructor<T = HTMLElement> = new (...args: any[]) => T;
export function ApolloQueryMixin<TBase extends Constructor, TCacheShape, TData, TVariables>
(superclass: TBase): ApolloQuery<TCacheShape, TData, TVariables> & TBase;

最后，我想导出一个 class 应用两个 mixins 并提供它自己的方法。 这是我遇到麻烦的地方

阿波罗查询.js

class ApolloQuery extends NotifyingElementMixin(ApolloQueryMixin(HTMLElement)) {
  /**
   * Latest data.
   */
  get data() {
    return this.__data;
  }

  set data(value) {
    this.__data = value;
    this.notify('data', value);
  }
  // etc
}

阿波罗查询.d.ts

import { ApolloQueryMixin } from "./apollo-query-mixin";
import { NotifyingElementMixin } from "./notifying-element-mixin";

export declare class ApolloQuery<TBase, TCacheShape, TData, TVariables>
extends NotifyingElementMixin(ApolloQueryMixin(HTMLElement)) {}

当我编译这个或使用我的 IDE 时，我收到错误：

error TS2339: Property 'notify' does not exist on type 'ApolloQuery'.

如何让 typescript 在混合 class 主体中获取我继承的方法？

Answer 1

这是我使用的mixin模式，我认为关键是返回构造函数：

import { LitElement, property } from "lit-element";

type Constructor = new (...args: any[]) => LitElement;

interface BeforeRenderMixin {
  beforeRenderComplete: Boolean;
}

type ReturnConstructor = new (...args: any[]) => LitElement & BeforeRenderMixin;

export default function<B extends Constructor>(Base: B): B & ReturnConstructor {
  class Mixin extends Base implements BeforeRenderMixin {
    @property({ type: Boolean })
    public beforeRenderComplete: boolean = false;

    public connectedCallback() {
      super.connectedCallback();
      if (!this.beforeRenderComplete)
        this.beforeRender().then(() => (this.beforeRenderComplete = true));
    }

    public async beforeRender() {
      return;
    }

    public shouldUpdate(changedProperties: any) {
      return this.beforeRenderComplete && super.shouldUpdate(changedProperties);
    }
  }

  return Mixin;
}

生成：

import { LitElement } from "lit-element";
declare type Constructor = new (...args: any[]) => LitElement;
interface BeforeRenderMixin {
    beforeRenderComplete: Boolean;
}
declare type ReturnConstructor = new (...args: any[]) => LitElement & BeforeRenderMixin;
export default function <B extends Constructor>(Base: B): B & ReturnConstructor;
export {};