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/[Abejide Femi Jr]\s/

Posted on May 20, 2018

Beginners Guide To Fetching Data With (AJAX, Fetch API & Async/Await)

#javascript #beginners #api #tutorial

Introduction

In this tutorial, I will be explaining how to fetch data asynchronously from an external API using web technologies like AJAX, Fetch API and Async/Await.

How To Fetch Data From An External API

AJAX

AJAX stands for Asynchronous Javascript and XML, it is a set of web technology to send and receive data asynchronously from a client or server, it is done behind the scene and you don't need to reload the webpage, JSON(Javascript Object Notation) have actually replaced XML(eXtensible Markup Language), most of the API's returns JSON data, AJAX can also return plain text.

Below is a description of how AJAX works

Request is being sent by making an AJAX call, Data in JSON format is being fetched asynchronously from the server and page content is being updated without reloading your webpage, we can fetch data from our local machine or server, public API.
I'll be demonstrating in the code below how to get data from Github API, an external API with AJAX.

    //Create the XHR Object
    let xhr = new XMLHttpRequest;
    //Call the open function, GET-type of request, url, true-asynchronous
    xhr.open('GET', 'https://api.github.com/users', true)
    //call the onload 
    xhr.onload = function() 
        {
            //check if the status is 200(means everything is okay)
            if (this.status === 200) 
                {
                    //return server response as an object with JSON.parse
                    console.log(JSON.parse(this.responseText));
        }
                }
    //call send
    xhr.send();
    //Common Types of HTTP Statuses
    // 200: OK
    // 404: ERROR
    // 403: FORBIDDEN

Below is the data

Fetch API

It is the newest standard for dealing with HTTPRequest, it is part of the window object, and we can easily fetch data from an external API as well.Fetch returns Promises
I'll be demonstrating in the code below how to get data from Github API, an external API with Fetch API.

    //call the fetch function
    fetch('https://api.github.com/users')
    .then(res => res.json())//response type
    .then(data => console.log(data)); //log the data;

Below is the data

Async/Await

It is part of the ES7 standard, it is now fully implemented in Chrome, we add async to the function and it returns a Promise.
I'll be demonstrating in the code below how to get data from Github API, an external API with Async/Await.

    async function getData() 
        {
            //await the response of the fetch call
           let response = await fetch('https://api.github.com/users');
            //proceed once the first promise is resolved.
           let data = await response.json()
            //proceed only when the second promise is resolved
            return data;
        }
//call getData function
getData()
.then(data => console.log(data));//log the data

Below is the data

Note

Any of the three methods can be used to fetch data, i actually prefer to use Fetch API, and there are several methods(axios, superagent e.t.c) apart from three methods, not discussed in this context, API's are different, how request is being taken and how response is being served differs, documentation is being provided for external API's to guide you.
I hope you enjoyed the tutorial, Thanks For Reading.

Top comments (36)

Mattias Petter Johansson • May 21 '18 • Edited

Note that response.json() returns a PROMISE. This is a common misconception. This article is a wee bit misleading in the async / await example, the data variable will be a promise but the example sort of makes it seem like response.json() is sync by not using await in front of the call.

/[Abejide Femi Jr]\s/ • May 21 '18

Thank you for spotting that out Mattias, it was a mistake, and the code as been edited.
Cheers.

Ronaldo Peres • Jan 1 '19

What is a Promise?

Alvaro Lamadrid • Apr 23 '19 • Edited

Take a look at MDN

developer.mozilla.org/en-US/docs/W...

Itachi Uchiha • May 21 '18 • Edited

Is there a way extract data from promise? For example, I don't want to use like this:

blah().then()

Maccabee • May 24 '18

You can await Promises.

const data = await blah();

That's how async/await compile with babel, into Promises.

Itachi Uchiha • May 24 '18

Thanks a lot. It worked :) Why I didn't try that. I think I was confused.

Pierre Joubert • May 24 '18

Ah much better xD

Pierre Joubert • May 24 '18

Do you not like the syntax? Or do you not want to deal with promises?

Itachi Uchiha • May 24 '18

I just wonder about assign result to a variable. I don't wan't to use then all time. For example:

const myResults = fetch('site.com')
   .then(resp => resp.json())
   .then(obj => obj)

console.log(myResults)
// { name: 'John', surname: 'Doe' }

Pierre Joubert • May 24 '18 • Edited

I just did this and it seemed to work:

var foo = null;
fetch('https://jsonplaceholder.typicode.com/posts/1')
   .then(resp => resp.json())
   .then(obj => foo = obj)

Then foo is accessible object like: foo.title
"sunt aut facere repellat provident occaecati excepturi optio reprehenderit"

Itachi Uchiha • May 24 '18

Thanks a lot. That's exactly what I want.

/[Abejide Femi Jr]\s/ • May 21 '18

don't know of any, apart from .then(), and .catch() -> for errors.

Eri Pançi • May 25 '18

Great article. It inspired me to experiment with API's since I'm in a period of learning Javascript. But doing a small project I got a problem, and since I didn't find an article online, I thought to ask here, hope I'll be clear:
Is there a possibility to make the async function and getData in different functions or objects?

Because in your example both these are immediately after one another. But after some time my code gets messy, so I wanted to make the function and the call in different objects.

Thank you.

/[Abejide Femi Jr]\s/ • May 25 '18

Hello, can you share your code

Eri Pançi • May 25 '18

since I'm working on Glitch, here is the full project: glitch.com/edit/#!/titanium-freeze

As you can see, inside the function getMovies it's async function and getData(). Can I make these two not inside one function but instead in two? One can get the data, the other can show it?

Thank you.

/[Abejide Femi Jr]\s/ • May 25 '18 • Edited

Can't access that URL, can you paste your code here please, or possibly push to GitHub and send the URL

Eri Pançi • May 25 '18

Strange. Anyway here it is in Github: github.com/erip2/MovieApp/

/[Abejide Femi Jr]\s/ • May 26 '18 • Edited

firstly, what are the datas you are trying to get from the API, i can also see you are trying to persist to sessionstorage, es6 classes could make the code look cleaner a bit tho, have a separate class for your ui, another class for you Session or local storage, then another class for the Movie.

Eri Pançi • May 26 '18

The data I'm getting from API is an array of movie titles the user search. Then when user clicks for details, I save the movie ID in sessionStorage to open a new window with that movie details.

That was exactly why I asked, to do these in different places in my code. Could I do these in different objects or should I read about JS classes since I don't know them very well to use it?

Thanks again.