Today I Learned - Rocky Kev

TIL how to convert a Callback to a Promise

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TAGS: callback promises advanced

How to convert a Callback to a Promise

Standard Callback:

function getTheThing(thingToGet, successCallback, failureCallback) {
  // get the thing
  const thing = someDatabaseQuery(thingToGet);

  if (thing) {
    // on success
    successCallback(thing);
  } else {
    // on failure
    failureCallback(thing);
  }

  // better version
  // return (thing) ? successCallback(thing) : failureCallback(thing);
}

If we are successful, it goes to the successCallback. If it fails, it goes to the failureCallback.

Callback functions work well for simple asynchronous operations, but can become difficult to manage and lead to "callback hell" when dealing with more complex operations.

Why switch over to a promise?

  1. Nested callbacks can quickly become difficult to read and understand.
  2. Callback functions can be error-prone when not properly implemented, such as failing to handle errors.
  3. It can be difficult to know when all callbacks have completed, or to handle errors that occur during a series of callbacks.

So let's modernize it by converting a standard callback into a Promise.


function getTheThingAsync(thingToGet){
	return new Promise((resolve, reject) => {

        getTheThing(thingToGet => {
            const thing = someDatabaseQuery(thingToGet);
            if (thing) {
                resolve(thing)
            } else {
                reject(new Error("Wasn't able to do it"))
            }
			})
    )
}

// using the promise
getTheThingAsync()
.then(result => console.log(result))
.catch( error => console.error(error));

A Refresher on Javascript Callbacks and Promises

Related TILs

Tagged: callback

TIL how to convert a Callback to a Promise

Callback functions work well for simple asynchronous operations, but can become difficult to manage and lead to 'callback hell' when dealing with more complex operations. Promises follow a specific pattern.

TIL how to convert a Callback to a Promise

Callback functions work well for simple asynchronous operations, but can become difficult to manage and lead to 'callback hell' when dealing with more complex operations. Promises follow a specific pattern.

TIL how to convert a Callback to a Promise

Callback functions work well for simple asynchronous operations, but can become difficult to manage and lead to 'callback hell' when dealing with more complex operations. Promises follow a specific pattern.