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DemoWebApp - Fun with APIs!!

My name is Talia and I set out on a mission to create the coolest, sleekest weather app ever devised by humankind. I ended up making a web app that fetches and displays weather data from the OpenWeatherMap API. Check it out at

APIs are great

API stands for Application Program Interface. The actual definition of this is pretty broad - APIs are basically a set of operations with specific inputs/outputs that let you interact with something, like a database, web service, or hardware (see here for more info if you're hardcore). In this case, we will be using Web APIs, which allow you to send and receive data from a web service. For example, let's say you wanted to display Jay Z's Twitter feed on your website because he is a beautiful wordsmith. You could use the Twitter API to grab the tweet history of a specific user (in this case, Jay Z aka Shawn Carter aka Hova). Most large-scale software companies like Google, Twitter, Facebook (and HubSpot!!) have APIs that let you use their services and data in your own applications. Also, many different kinds of data can be accessed via an API - weather, movie information/reviews, sports stats, restaurants, maps, Jay Z's sick rhymes, etc. If you're wondering if an API exists for some form of data, give it a Goog. Chances are, if it's within reason there's an API for that.

How (most) Web APIs work

You can grab information from a web service using HTTP, which is how you would access just about any other website. Just like how you access Facebook by sending an HTTP request to, most web APIs can be accessed by sending an HTTP request to some URL. In this repo, I send a request to There are a couple types of HTTP requests: GET, POST, DELETE, PUT, etc. GET is the most commonly used type - it's for when you want to retrieve data from a service, like reading a specific item from a database. POST is for sending data to a service, usually to create something new in a database, so POST requests also contain a payload with the information you want to send. Feel free to read up on what the other methods do here. This app uses a GET request to grab today's weather data for a given city - note that my API request is read-only, it doesn't actually change any of OpenWeatherMap's data.

How to use an API

All APIs are different

Most Web APIs work the same way with HTTP but all have their own specifications on how to interact with them. Each API has its own URL structure and rules on what kinds of requests it will accept. To get the weather for Boston, I send a GET request to In general, you start off with some base URL - - and add more specific paths and query parameters to tell the API exactly what information you want. So in this case, adding data/2.5/weather means you want the weather for some location. Adding id=4930956 means you want the weather for the city with id 4930956, which is Boston (the OpenWeatherMap documentation has a list of all major cities and the ids they correspond to). Adding units=imperial means you want it in imperial (American) units since I want to display the temperature in Fahrenheit rather than Kelvin (which is the default for this API). Kelvin is for nerds.

The data that is returned will also be totally different between APIs. Most web APIs return data in the JSON format, which is just a very simple object format i.e. {key: value}. OpenWeatherMap returns a large JSON object, which looks like this:

  "weather":[{"id":500,"main":"Rain","description":"light rain","icon":"10d"}],
  "base":"cmc stations",

A different weather API would probably return similar data, i.e. temperature, wind speed, chance of rain, chance of Beyonce sightings, but it would return a JSON object in a completely different format. Either way, you can easily take that object and pull out the information you want.

Documentation is your best friend

The only way to know how to use a certain API like this is to go to its website and read the documentation there. Any decent API will provide instructions and documentation for the different kinds of requests you can send and what information will be sent back. OpenWeatherMap has extensive docs detailing what kind of weather data you can grab and what will be returned. As the saying goes: "Docs are a girl's best friend".


Most APIs require some form of authorization to make sure that not just anyone can send a request to it. Just like how not just anyone can be part of Taylor Swift's lady squad. Usually, you can get authorization by making an account with the service and getting an API key (sometimes called an access token). This is a special string that you send along with the request - usually as a query parameter like apiKey=[your api key] - that lets the API know that you're an authorized user. APIs all have their own way of doing this and have instructions on how to get started, another reason to read the documentation nudge nudge

Important: API keys are sensitive information. Protect them like a mama bear protecting its cubs. Ok well maybe that's a bit of a stretch. You don't want just anyone to see them, so it's good practice to NOT expose them in your code on GitHub. I hid my API key by setting it as an environment variable (which is just a special named value) on Heroku and accessing it in my app, under the name API_KEY. I'll explain how to do this in the tutorial. This way, I got 99 problems but risk of someone abusing my API key definitely ain't one.

Integrating an API in your app

To access an API and use its data in your app, you'll need a way to actually send a request to it and handle the returned data. If you take a look at public/js/main.js you'll see my app uses a method called ajax to send the request to OpenWeatherMaps's servers. The method is just an implementation of the AJAX technique for sending and receiving data from a server somewhere else (see here for more info). It also handles the returned information in 2 types of functions: a success handler and an error handler. The success handler function gets called when the request goes smoothly comes back with the desired data. It takes the weather data, pulls out the information I want, and displays it on my webpage using jQuery. The error handler function is called when something goes wrong - this is super super important when using APIs, requests can sometimes run into an error and in most cases will return some form of error message.

Also important: My app doesn't work if you access my page at HTTPS rather than HTTP - This is because my API call uses plain HTTP which is not allowed on an HTTPS page. I tried looking into a solution, but for the sake of simplicity I would just have people access my site at the http address rather than https. It's lazy but since the purpose of this demo is to demonstrate basic API usage, let's not worry about it :)

Tutorial Tyme

So here's the good stuff - how to actually build this krazy app. Each step will include instructions for OpenWeatherMap API if you wanna use it and general instructions that should apply to most APIs where necessary. If you decide to use a different API and you're getting stuck with how to use it don't hesitate to ask one of us lovely volunteers for a hand! If you are using OpenWeatherMap feel free to just copy/paste from my code, but the code for this tutorial will look a little different and simpler.

Note: this tutorial assumes that you have Zoe's demo app cloned, and that you have Heroku up and running ANOTHER NOTE: if you're not that familiar with APIs I'd recommend staying away from more complicated APIs like Google and sticking with something more simple, like OpenWeatherMap!

  1. Choose your API. What kind of data do you want to use? The world is your oyster. If you're feeling like just getting a chill practice run in API World for today, use OpenWeatherMap!
  2. Most API sites, including OpenWeatherMap, will want you to create an account first before using their services, create that account!
  3. Look around in your shiny new account for anything about API keys or access tokens, in OpenWeatherMap it's here Chances are it'll be a bunch of numbers and/or letters all jumbled up.
  4. Grab that API key and run heroku config:set API_KEY=whateveryourapikeyis in your terminal (Substituting whateveryourapikeyis for whatever your API key is)
  5. Then run heroku config:get API_KEY -s >> .env. This way you can use API_KEY in your local environment for testing!
  6. Go into index.ejs and make sure that <script>var apiKey = '<%= process.env.API_KEY %>';</script> is in your head tag if it's not already there! Make sure it comes before <script src="/js/main.js"></script>. The order matters here because main.js will want to use API_KEY.
  7. To actually call the API, we'll need jQuery to use its ajax method and then set the retrieved data in our HTML (but if there's a different library you like to use for making HTTP requests go for it!). In that same head tag, insert <script src=""></script> before the main.js script tag.
  8. First, let's display the weather for one city. How about Boston! If you're using a different API you can mirror what I'm doing while keeping it relevant to the type of data you're dealing with - your API's abilities and documentation will be different. Or you can off-road and build whatever you'd like! We'll just display the city and temperature for now. Insert <div class="city"></div><div class="temp"></div> in your HTML body.
  9. Time to actually use the API in main.js! At the top of your main.js file insert the following:
$(document).ready(function() {
  1. Now we'll create a function called getWeather that will retrieve the weather for Boston. We'll have to build the URL for the API request according to OpenWeatherMap's specifications. Note that we're using apiKey in here which was defined in the head of index.ejs and that we're setting the id to 4930956, aka Boston. When the API call is finished and returns the weather data, we'll want to pull out the information we want and insert it in our HTML in our success function. Notice that we set the HTML text with our results using jQuery, which is designated by the $ symbol.
function getWeather() {
  var url = '' + apiKey;
  $.ajax(url, {
    success: function (data) {
      $('.temp').text(data.main.temp + ' °F');
  1. Give it a run! It should display the Boston weather when you first load your site.
  2. OK. Now, let's try to make it so you can search for any location. We need a search bar to type queries into and a button that'll fire the search. The button should have a function as its onClick handler that starts the search, we'll call it searchWeather. You'll want to add this to your HTML body:
<input class="search" type="text" placeholder="Enter city name..." />
<button type="button" onclick="searchWeather()">
  1. In main.js, add a searchWeather function that grabs whatever is in your search bar and then calls your API accordingly with that value:
function searchWeather() {
  var searchQuery = $('.search').val(); // grab value from search input
  1. Now, you'll need getWeather to take a single argument - searchQuery - and send that value in your URL up to the API so it knows to search for the weather at a location matching your query. Instead of throwing units and id and APPID into the same URL string, we can make an object that represents the query parameters to send along to the API. jQuery has a method called param that takes an object like {foo: 'bar', baz: 'qux'} and returns a string with that object's keys and values in the right format for a URL like foo=bar&baz=qux. If searchQuery exists, we want to put it into our URL. Otherwise, we will default to the city id for Boston.
function getWeather(searchQuery) {
  var url = ''; // url for the API
  var params = {
    APPID: apiKey,
    units: 'imperial'
  if (searchQuery) {
    params.q = searchQuery;
  } else { = 4930956
  $.ajax(url + $.param(params), {
    success: function (data) {
      $('.temp').text(data.main.temp + ' °F');
  1. Try re-running your app. The Boston temperature should show by default as it did before. Type in a different city anywhere in the world and see if it works!!!!
  2. API calls don't always go smoothly. We need to add some error messaging in case things go wrong so the user isn't left in the dark. Normally we would want to include details as to what went wrong but a generic error message will do for now. In your HTML, add this to your HTML body: <div class="error-message"></div>
  3. Modify your AJAX call to add an error handler:
$.ajax(url + $.param(params), {
  success: function (data) {
    $('.temp').text(data.main.temp + ' °F');
  }, error: function (error) {
    $('.error-message').text('An error occurred!');

You can test your error handler by messing up the API URL in your ajax call on purpose. The API call should result in a 404 which should be caught in your error handler. If you see your error message after re-running the app, it's good to go!

Woo you did it! That was a wild ride. Try taking this further - you can display more data in your HTML, like precipitation or wind speeds. All you have to do is access the other data in the returned JSON object from the API call. Try making this look better too! You can use CSS, Bootstrap, and other libraries to make your app look sleeker and more professional.


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