Waiting for promises inside the object to resolve

user_7569893 0
Viewed 1611

I have an object that has promises as its values. The object fields could have different types of values such as functions, promises, strings, numbers, or another object. How do I implement a function which waits for all the promises in the object to resolve?

const asyncFunction = () => {
  return Promise.resolve("Resolved!")
}
const nonAsyncFunction = () => {
  return "Resolved!"
}
const awaitObjectWithPromise = (obj) => {
  // Returns a promise which waits for all
  // the promises inside "obj" to be resolved.
}
let obj = {
  key1: asyncFunction(),
  key2: nonAsyncFunction(),
  key3: "Some Value",
  parent1: {
    key1: asyncFunction(),
    key2: nonAsyncFunction(),
    key3: "Some Value"
  }
}

awaitObjectWithPromise(obj).then((obj) => {
  console.log(obj);
  // Should output:
  // {
  //     key1: "Resolved!",
  //     key2: "Resolved!",
  //     key3: "Some Value",
  //     parent1: {
  //         key1: "Resolved!",
  //         key2: "Resolved!",
  //         key3: "Some Value"
  //     }
  // }
})

es6-promise async-await javascript
2 Answers

You can iterate through the keys of the object and solve the promises.

const asyncFunction = () => {
  return Promise.resolve("Resolved!")
}
const nonAsyncFunction = () => {
  return "Resolved!"
}
const awaitObjectWithPromise = async(obj) => {
  for (let prop in obj) {
    // If the propriety has a 'then' function it's a Promise
    if (typeof obj[prop].then === 'function') {
      obj[prop] = await obj[prop];
    }
    if (typeof obj[prop] === 'object') {
      obj[prop] = await awaitObjectWithPromise(obj[prop]);
    }
  }
  return obj;
}

let obj = {
  key1: asyncFunction(),
  key2: nonAsyncFunction(),
  key3: "Some Value",
  parent1: {
    key1: asyncFunction(),
    key2: nonAsyncFunction(),
    key3: "Some Value"
  }
}

awaitObjectWithPromise(obj).then((obj) => {
  console.log(obj);
});

user_103873960

In the accepted answer, I was not happy with some things:

  • an error is thrown if one of the fields is null or undefined;
  • the input value cannot be a Promise;
  • lack of parallelism of waiting for Promises;

To fix these things, I changed the function:

const promiseAll = async (obj) => {
    if (obj && typeof obj.then == 'function') obj = await obj;
    if (!obj || typeof obj != 'object') return obj;
    const forWaiting = [];
    Object.keys(obj).forEach(k => {
        if (obj[k] && typeof obj[k].then == 'function') forWaiting.push(obj[k].then(res => obj[k] = res));
        if (obj[k] && typeof obj[k] == 'object') forWaiting.push(promiseAll(obj[k]))
    });
    await Promise.all(forWaiting);
    return obj;
}

Maybe for someone, it will be useful.

user_115101810
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