I have found an interesting algorithm that I would like to know if it is really necessary or if there is a way to improve it because the code is very confusing. Essentially, the getValue method can be called at any time (it's part of library code) and it is necessary to guarantee that the call to the server is made only once. If someone need value while it's being loaded from server, the promise should wait until server response. The solution in this case is to accumulate the method calls in a queue and then, when the server call promise is resolved, execute everything accumulated.

I understand that due to the asynchrony of the language something like this is necessary, but can there be something better?

Demo code:

function getValueFromServer() {
  console.log("get value from server");
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve("value");
    }, Math.floor(Math.random() * 10));
  });
}

var singObj = {
  value: "",
  working: false,
  queue: [],
  getValue: function() {
    if (!this.working && this.value !== "") {
      console.log("not working and value exists");
      return value;
    }

    return new Promise(async(resolve, reject) => {
      console.log("queue resolution...");
      this.queue.push(resolve);

      if (!this.working) {
        this.working = true;
        this.value = await getValueFromServer();
        this.working = false;
        this.queue.forEach((f) => {
          f(this.value);
        });
      }
    });
  }
}

function getValueUsage() {
  var result = Promise.allSettled([singObj.getValue(), singObj.getValue(), singObj.getValue()]);
  console.log(result);
  var result = Promise.allSettled([singObj.getValue(), singObj.getValue(), singObj.getValue()]);
  console.log(result);
}

getValueUsage();

<iframe name="sif1" sandbox="allow-forms allow-modals allow-scripts" frameborder="0"></iframe>

CodePudding user response：

This can be done much simpler indeed. A promise already does hold onto its result value forever, and you can call .then() on the same promise multiple times. So all you need to do is

var singObj = {
  promise: null,
  getValue: function() {
    if (!this.promise)
      this.promise = getValueFromServer();
    return this.promise;
  }
};