Promises

Promises Explained

Overview#

In our previous section we saw how to make a request to the dog API and get some data.

fetch("https://dog.ceo/api/breeds/image/random")
  .then((response) => response.json())
  .then((data) => console.log(data));

We can see that we are using the fetch function to make a request to the dog API. The fetch function returns a promise. A promise is an object that represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.

so when we use a fetch method we get a promise... In this promise we have two methods then and catch. The then method is used to handle the success of the promise and the catch method is used to handle the failure of the promise.

fetch("https://dog.ceo/api/breeds/image/random")
  .then((response) => response.json())
  .then((data) => console.log(data))
  .catch((error) => console.log(error));

the same senario we had when we sent someone to get us some salt

the first .then is used to handle a successful promise and the second .then is used to handle the data that is returned from the promise. The .catch is used to handle the error that is returned from the promise. the catch catches errors and we can do something with the error maybe notify the user or whoever made the request something has gone wrong...

Implementation#

So I hope this has dimisfied the mystery of promises and how they work.

Tradeoffs#

Exercise#

do we have a nicer way to work with promises? yes we do an that't the topic for the next lecture. Async and Await....