website/src/content/resources/language/javascript/promises/simplifying-promises.md

authors, created_at, title

authors	created_at	title
Xetera#0001	2019/07/26	Simplifying Promises

The first naive attempt, using new Promise for something that already returns a promise.

function doAsync(number) {
  return new Promise(function (resolve, reject) {
    doDatabase().then(function (dbResult) {
      otherDbFunction(dbResult).then(function (secondResult) {
        resolve(secondResult + 10);
      });
    });
  });
}

Turns out you don't need new Promise if you're working with a function that already returns a promise, you can just return the original thing.

function doAsync(number) {
  return doDatabase().then(function (dbResult) {
    otherDbFunction(dbResult).then(function (secondResult) {
      return secondResult + 10;
    });
  });
}

You also don't have to nest .then functions, the whole point of promises is that they allow you to chain them sequentially.

function doAsync(number) {
  return doDatabase()
    .then(function (dbResult) {
      return otherDbFunction(dbResult);
    })
    .then(function (secondResult) {
      return secondResult + 10;
    });
}

you also don't have to create a new function just to pass in one variable, you can pass in the entire function itself to the then block

function doAsync(number) {
  return doDatabase()
    .then(otherDbFunction)
    .then(function (secondResult) {
      return secondResult + 10;
    });
}

And you don't need those returns if you just have ES6 arrow functions

const doAsync = (number) =>
  doDatabase()
    .then(otherDbFunction)
    .then((secondResult) => secondResult + 10);

Wow, that last one looks a lot cleaner to me than the first. Keeping that in mind, maybe we could be making some of our other functions cleaner as well