Getting more hands-on with APIs

Calling / Using an API

When do I need to do this?

You need to request information to some external service (e.g. getting the current weather, fetching your facebook posts, etc.)
You need to communicate with a service someone else built (e.g. your teammate)

This is usually done through the aforementioned HTTP requests. Each language has a different way of making these requests.

Python

requests library → https://requests.readthedocs.io/en/master/

This library makes it dead simple to make HTTP requests. If you have Python installed already, you can get this library by typing

pip install requests

You can then use requests in Python by importing it.

import requests

# make a GET request to the GitHub API and store
# the result in the variable r
r = requests.get('https://api.github.com/repos/psf/requests')

# r.status_code will tell you the status of the request
print(r.status_code) 
# should print out '200'

# you can then convert the actual body of the response into
# a python readable form (a dictionary in this case)
body = r.json()

# then you can get certain fields from the body
print(body["description"]) 
# should print out 'A simple, yet elegant HTTP library.'

JavaScript

XMLHttpRequest → This is a built-in JavaScript object that lets you make HTTP requests in Vanilla JavaScript! Example usage is as follows,

// create a function that tells JavaScript what to do
// after receiving a response from the server
function handleResponse () {
    // create a 'response' variable that contains the response data
    const response = this

    // print out the status of the request
    console.log(response.status)

    // get the body of the request and parse into JSON 
    // (allows JavaScript to easily manipulate the data)
    const body = JSON.parse(response.responseText)

    // print out the description field again
    console.log(body.description)
}

// create a new request object with the name 'r'
const r = new XMLHttpRequest();

// add an event listener so that we run 'handleResponse()' after the
// request 'r' loads
r.addEventListener("load", handleResponse);

// make the actual request to the resource using GET
r.open("GET", "https://api.github.com/repos/psf/requests");
r.send();

You can learn more about XMLHttpRequest here: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest

Axios → Axios is a Promise-based alternative to XMLHttpRequest that works in Node.js too :)) I'm not going to go into too much detail but it is definitely a more clean and easier way to do HTTP requests in JavaScript if you don't mind using external libraries. You can read more here: https://github.com/axios/axios

You can read a more detailed guide here: https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Introducti

Building your own API

When do I need to do this? →

You need to serve up some information (e.g. get user details from a database)
You need to cobble together a bunch of other APIs (e.g. get data from current weather and feed it into Google Search API)

The implementation vastly differs per language, but the main concept is the same: you create a HTTP server that listens for and responds to requests from the internet. Both Python and JavaScript have frameworks that make it simple to do just that. Going into the implementation of each is a little outside the scope of this guide, so instead we'll link a few good guides and tutorials that we've found to get you started.