Using JavaScript to Fetch Data With APIs | by Andrew Stahl | Jun, 2022

Nice newbie information to APIs with an easy-to-follow real-world venture.

Title Picture; In the present day’s Matter: Fetch Requests with API


  • Introduction to APIs
  • Introduction to fetch requests
  • Overview of a venture that leverages this performance: a single-page utility that produces a date for any US vacation and grabs a reality for that date in historical past.

What’s an API?

If you’re an online developer, understanding easy methods to work with an API is an important talent in knowledge dealing with. API stands for Software Programming Interface. It permits two computer systems to attach to one another and switch knowledge. In addition they makes it very easy to tug knowledge into your utility that you don’t retailer domestically.

For instance, if you’re constructing an internet site and also you wish to pull in climate info or the most recent inventory costs, you may select easy methods to deal with that. You may obtain all that knowledge onto your individual servers and have your web site connect with them, which might require you to have sufficient house in your servers to deal with that knowledge and also you would wish to constantly replace it as nicely. The opposite possibility could be to discover a firm or database that has this knowledge and has API performance that permits you to pull, or fetch, knowledge into your utility.

There are a few caveats to utilizing APIs that you ought to be conscious of:

  • They don’t seem to be at all times free, so in some instances, it is advisable have a paid membership to entry these APIs. Your membership may enable you a sure variety of knowledge pulls per day/week/month/yr, so you should verify that earlier than your build-out.
  • Pulling knowledge from one other distant server may take a bit longer than pulling knowledge from your individual server. With that latency, it’s best to issue that into how your webpage masses so you may nonetheless have most of your performance populate (a median person will solely wait 3 seconds for a web page to load earlier than shifting on)

APIs are a reasonably meaty subject, however we’ll exhibit how they will work at a base stage. I’ve developed a easy single-page application that utilizes two free APIs to pull data on historical/future holidays.

Let’s dive in!

The venture I constructed will enable the person to select a US vacation and a yr and produce the day for that vacation and a enjoyable reality.

To do that, I used two free APIs, Nager.Date and Wikipedia. There’s additionally a button that enables the person to see what number of days are left till we attain that vacation (assuming it’s sooner or later).

I’ve included a fast visible of the performance of the web page earlier than we dive into the code:

Gif displaying performance of the venture

I have to fetch knowledge for my web site in just a few other ways:

  • When the web page masses, I want to make use of the Nager API to populate the dropdown for holidays (that is higher than hard-coding the times in as a result of I’ll at all times have an up-to-date checklist of holidays as an alternative of the checklist turning into stagnant over time)
  • After the person submits the vacation and yr, I want to make use of the Nager API to tug within the acceptable date for that vacation.
  • After that date is populated, the positioning will routinely fetch knowledge utilizing the Wikipedia API to tug a enjoyable reality for that day in historical past.

To start out constructing the code, I want to put out the totally different features to make it occur. I additionally want so as to add occasion listeners onto parts on the webpage so the applying is aware of when to fetch knowledge.

First Fetch

Specializing in them separately, let’s first take a look at what we want for the fetchHolidays perform. Right here’s the code that we’ll break down line by line:

I left parts of the code out as a result of I would like this weblog to focus totally on fetching API knowledge. For extra info on the remainder of the code, you may go to my Github repository for this project.

Now allow us to begin breaking this down:


When speaking with an API, you should utilize a “fetch” request. You may see that I’m making a request to fetch knowledge for US holidays in 2022 (you may change each the yr and the nation code to fetch different holidays).

Once you do that, you’re calling the API and what you’ll get in return is just not the information for these parameters however a promise to return that knowledge finally.

This return worth is essential as a result of it can dictate how it’s best to write the remainder of the code for this request.

if (response.standing !== 200)
console.warn("Seems to be like we did not get a very good request. Request
Code: " + response.standing);


return response.json();

Allow us to take this line by line.

First, you may see that we begin off with utilizing .then, which follows thefetch request and tells the pc, “fetch the information, then if you obtain a response for that knowledge, run the subsequent little bit of code.”

The one enter for a .then assertion is a perform. On this case, I’m operating a perform that checks what the response has been for that fetch request.

There are totally different codes for several types of responses, however the one one we’re interested by is a 200 response, which implies that it was profitable (for extra particulars on HTTP response codes, go to MDN Web Docs for HTTP response status codes).

If we don’t get a 200, that implies that the fetch request didn’t fairly attain or return what we wished, so we’re simply going to place this warning within the console on cancel out of the perform with a “return” assertion.

If we do get a 200 response standing code, we’re in enterprise! Remember the fact that the returned response from the server won’t be in a usable format, so we have to use our helpful .json() perform to return that response in a JSON format (which we will work with).

.then(knowledge => knowledge.ForEach(vacation => 
//Further code to seize the vacation choose dropdown and add every
//vacation to that choose dropdown

Lastly, we’re going to daisy-chain one other .then as a result of after receiving the response in a JSON format from our earlier .then, we will lastly work with this knowledge.

As a substitute of an everyday perform() notation, I used an arrow perform because the enter. You should use common notation, arrow notation, or a callback perform for these .then inputs (extra on callback features in a bit, as they’ll be essential to the effectivity of our code).

For this perform, I’m getting the information from the earlier .then assertion, which might return an array-like object for this API, and I’m going to iterate over that array to search out every vacation.

I gained’t submit the remainder of the code right here since that doesn’t should do with fetch requests, however you may test it out on my Github repository for this project.

Second Fetch

Now we’re going to undergo the second fetch request for pulling the suitable date for the chosen vacation/yr

You may see that it appears extremely just like the primary fetch request that we made with minor variations:

  • As a substitute of utilizing the present yr within the first fetch, we’re utilizing the yr that the person chosen within the dropdown
  • The perform after the second .then assertion manipulates the information another way

Abstracting The First Two Fetch Requests

So how can we comply with the DRY technique (Don’t Repeat Yourself) and hold our code intact? In comes the callback perform! It is a means that we will go a perform as a parameter of one other perform. In accordance with W3 colleges:

A callback is a perform handed as an argument to a different perform…This method permits a perform to name one other perform…

We will hold the fetch request as a separate perform. As soon as it returns knowledge, we will name the opposite features to step in and do what they should do. The fetch must know the yr we’re fetching and the callback perform that must be known as after the information runs.

Let’s see this in motion utilizing the code on the high with this new abstraction:

Third Fetch

The third and final fetch that we make is to Wikipedia to seize a enjoyable reality for that day in historical past. We may summary it even additional to be included in our different fetchData perform, however I’m going to maintain this separate.

This perform will hearth proper after the applying grabs the date for the chosen vacation.

We have to know the month and day to populate the API URL. Right here’s a fast breakdown of this code:

  • The fetch is fetching knowledge from the Wikipedia API and returning a promise to offer a response for that knowledge.
  • The primary .then comprises a fast arrow perform that takes the response returned from the earlier code and returns the JSON model of that response.
  • The second .then takes the information, finds what number of parts are in that array (which signifies what number of info Wikipedia shops on that day), after which picks a random reality from that checklist to show.

This fetch structure was a lot easier than the earlier ones above, which was intentional for the aim of this weblog. There are just a few other ways to write down it, however they need to comply with the identical construction to supply the supposed outcome.

More Posts