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

authors, created_at

authors	created_at
Xetera#0001	2019/07/26

Simplifying Promises

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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 do 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