检查请求是否已经按承诺完成答案

【问题标题】：Check if the request is already done on promise检查请求是否已经按承诺完成
【发布时间】：2020-11-06 01:28:45
【问题描述】：

我在一个文件中有这个函数：

setToStorage() {
    this.settingsService.getSettings().then((settings: any) => {
        localStorage.setItem('const', JSON.stringify(settings));
    });
}

现在在另一个文件中：

if (!localStorage.getItem(STORAGE_ACCOUNT_ATTRIBUTES)) {
        this.accountService.setToStorage();
}
const account = JSON.parse(localStorage.getItem('const'));

问题是在从本地存储中获取const 之前，如何知道setToStorage 是否完成？因为如果我做JSON.parse(localStorage.getItem('const')) 但setToStorage() 没有完成，我将有一个空值。请帮我。提前谢谢！

【问题讨论】：

标签： angular typescript promise angular8

【解决方案1】：

这是一个使用函数缓冲区和布尔状态变量的示例。

当尚未调用 Set 时，我们会将 Get 调用存储到一个数组中并等待。

当 Set 最终被调用时，我们将解析所有存储的 Get 调用。

下面的代码是快速创建的，并且在很大程度上是可以改进的。

使用一个实用函数，该函数能够处理对您的函数（Set/Get）的同步调用，并提供函数指针

function getRndInteger(min, max) {
  return Math.floor(Math.random() * (max - min)) + min;
}

class LocalStorage {
  constructor() {
    this.valueHasBeenInitialized = false;

    // Keep the functions that are waiting for the values to be initialized
    this.functionsKeeper = [];
  }

  // Call all the functions that are waiting to be resolved
  unlockKeptFunctions() {
    this.functionsKeeper.forEach(({
      func,
      resolve,
    }) => {
      func.call(this, resolve);
    });

    this.functionsKeeper = [];
  }

  setToStorage() {
    return new Promise((resolve) => {
      setTimeout(() => {
        console.log('> Resolve setToStorage');

        // INSERT THE CONTENT OF THE SET FUNCTION HERE **

        this.valueHasBeenInitialized = true;

        this.unlockKeptFunctions();

        resolve();
      }, getRndInteger(1500, 3000));
    });
  }

  /**
   * We want the get to be executed only after a setToStorage
   */
  getFromStorage() {
    return new Promise((resolve) => {
      const func = (r) => {
        setTimeout(() => {
          console.log('> Resolve getFromStorage');

          // INSERT THE CONTENT OF THE GET FUNCTION HERE **

          r();
        }, getRndInteger(500, 1800));
      };

      if (!this.valueHasBeenInitialized) {
        console.log('getFromStorage() is waiting \
 for setFromStorage to be called');

        // Wait until the value has been initialized
        return this.functionsKeeper.push({
          func,
          resolve,
        });
      }

      func(r);
    });
  }
}

// Call get and set asynchronously
(async() => {
  const localStorage = new LocalStorage();

  await Promise.all([
    localStorage.getFromStorage(),
    localStorage.getFromStorage(),
    localStorage.getFromStorage(),
    localStorage.getFromStorage(),
    localStorage.setToStorage(),
  ]);
})();

【讨论】：