承诺解决后打字稿返回布尔值 [英] Typescript returning boolean after promise resolved

问题描述

我试图在承诺解决后返回一个布尔值，但打字稿给出错误提示

I'm trying to return a boolean after a promise resolves but typescript gives an error saying

get"访问器必须返回一个值.

我的代码看起来像.

get tokenValid(): boolean {
    // Check if current time is past access token's expiration
    this.storage.get('expires_at').then((expiresAt) => {
      return Date.now() < expiresAt;
    }).catch((err) => { return false });
}

此代码适用于 Ionic 3 应用程序，存储为 Ionic Storage 实例.

This code is for Ionic 3 Application and the storage is Ionic Storage instance.

推荐答案

你可以返回一个 Promise ，它会解析成这样的布尔值:

You can return a Promise that resolves to a boolean like this:

get tokenValid(): Promise<boolean> {
  // |
  // |----- Note this additional return statement. 
  // v
  return this.storage.get('expires_at')
    .then((expiresAt) => {
      return Date.now() < expiresAt;
    })
    .catch((err) => {
      return false;
    });
}

您问题中的代码只有两个返回语句:一个在 Promise 的 then 处理程序中，一个在其 catch 处理程序中.我们在 tokenValid() 访问器中添加了第三条 return 语句，因为访问器也需要返回一些东西.

The code in your question only has two return statements: one inside the Promise's then handler and one inside its catch handler. We added a third return statement inside the tokenValid() accessor, because the accessor needs to return something too.

这是一个工作示例 在 TypeScript 游乐场:

class StorageManager { 

  // stub out storage for the demo
  private storage = {
    get: (prop: string): Promise<any> => { 
      return Promise.resolve(Date.now() + 86400000);
    }
  };

  get tokenValid(): Promise<boolean> {
    return this.storage.get('expires_at')
      .then((expiresAt) => {
        return Date.now() < expiresAt;
      })
      .catch((err) => {
        return false;
      });
  }
}

const manager = new StorageManager();
manager.tokenValid.then((result) => { 
  window.alert(result); // true
});

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