Project: Weather App

Introduction

Use everything we’ve been discussing to create a weather forecast site using the weather API from the previous lesson. You should be able to search for a specific location and toggle displaying the data in Fahrenheit or Celsius.

You should change the look of the page based on the data, maybe by changing the color of the background or by adding images that describe the weather. (You could even use the Giphy API to find appropriate weather-related gifs and display them). Feel free to use promises or async/await in your code, though you should try to become comfortable with both.

  1. Set up a blank HTML document with the appropriate links to your JavaScript and CSS files.

  2. Write the functions that hit the API. You’re going to want functions that can take a location and return the weather data for that location. For now, just console.log() the information.

  3. Write the functions that process the JSON data you’re getting from the API and return an object with only the data you require for your app.

  4. Set up a simple form that will let users input their location and will fetch the weather info (still just console.log() it).

  5. Display the information on your webpage!

  6. Add any styling you like!

  7. Optional: add a ‘loading’ component that displays from the time the form is submitted until the information comes back from the API.

  8. Push that baby to github and share your solution below!


Material based on Erik Trautman | The Odin Project

Feedback

  • Is there anything we can help with up to this point? Do you have something to suggest about this chapter? Let us know in the comments below.

Async and Await

Introduction

Asynchronous code can become difficult to follow when it has a lot of things going on. async and await are two keywords that can help make asynchronous read more like synchronous code. This can help code look cleaner while keeping the benefits of asynchronous code.

For example, the two code blocks below do the exact same thing, they both get information from a server, process it, and return a promise.

function getPersonsInfo(name) {
  return server.getPeople().then(people => {
    return people.find(person => { return person.name === name });
  });
}
async function getPersonsInfo(name) {
  const people = await server.getPeople();
  const person = people.find(person => { return person.name === name });
  return person;
}

The second example looks much more like the kind of functions you are used to writing, however, did you notice the async keyword before the function declaration? How about the await keyword before server.getPeople()?

Learning Objectives

  1. How do you declare an async function?
  2. What does the async keyword do?
  3. What does the await keyword do?
  4. What is returned from an async function?
  5. What happens when an error is thrown inside an async function?
  6. How can you handle errors inside an async function?

The async keyword

The async keyword is what lets the javascript engine know that you are declaring an asynchronous function, this is required to use await inside any function. When a function is declared with async, it automatically returns a promise, returning in an async function is the same as resolving a promise, likewise, throwing an error will reject the promise.

An important thing to understand is async functions are just syntactical sugar for promises.

The async keyword can also be used with any of the ways a function can be created, said differently: it is valid to use an async function anywhere you can use a normal function. Below you will see some examples that may not be intuitive, if you don’t understand them, come back and take a look when you are done with the assignments.

  const yourAsyncFunction = async () => {
    // do something asynchronously and return a promise
    return result;
  }
 anArray.forEach(async item => {
   // do something asynchronously for each item in 'anArray'
   // one could also use .map here to return an array of promises to use with 'Promise.all()'
 });
server.getPeople().then(async people => {
  people.forEach(person => {
    // do something asynchronously for each person
  });
});

The await keyword

await is pretty simple: it tells javascript to wait for an asynchronous action to finish before continuing the function. It’s like a ‘pause until done’ keyword. The await keyword is used to get a value from a function where you would normally use .then(). Instead of calling .then() after the asynchronous function, you would simply assign a variable to the result using await, then you can use the result in your code as you would in your synchronous code.

Error Handling

Handling errors in async functions is very easy. Promises have the .catch() method for handling rejected promises, and since async functions just return a promise, you can simply call the function, and append a .catch() method to the end.

asyncFunctionCall().catch(err => {
  console.error(err)
});

But there is another way: the mighty try/catch block! If you want to handle the error directly inside the async function, you can use try/catch just like you would inside synchronous code.

async function getPersonsInfo(name) {
  try {
    const people = await server.getPeople();
    const person = people.find(person => { return person.name === name });
    return person;
  } catch (error) {
    // Handle the error any way you'd like
  }
}

Doing this can look messy, but it is a very easy way to handle errors without appending .catch() after your function calls. How you handle the errors is up to you, and which method you use should be determined by how your code was written. You will get a feel for what needs to be done over time. The assignments will also help you understand how to handle your errors.

Practice

Remember the Giphy API practice project? (If not, you should go back and complete the API lesson) We are going to convert the promise based code into async/await compatible code. Here’s a refresher of the code we are starting with:

<script>
  const img = document.querySelector('img');
  fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'})
    .then(function(response) {
      return response.json();
    })
    .then(function(response) {
      img.src = response.data.images.original.url;
    });
</script>

Since await does not work on the global scope, we will have to create an async function that wraps our API call to Giphy.

<script>
  const img = document.querySelector('img');

  async function getCats() {
    fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'})
      .then(function(response) {
        return response.json();
      })
      .then(function(response) {
        img.src = response.data.images.original.url;
      })
  }
</script>

Now that we have a function that is asynchronous, we can then start refactoring from using promises to using await:

<script>
  const img = document.querySelector('img');

  async function getCats() {
    const response = await fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'});
    response.json().then(function(response) {
      img.src = response.data.images.original.url;
    });
  }
</script>

Since response is still the same object we have passed to the .then() block at the start, we still need to use the .json() method, which in turn returns a promise. Because .json() returns a promise, we can use await to assign the response to a variable.

<script>
  const img = document.querySelector('img');

  async function getCats() {
    const response = await fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'});
    const catData = await response.json();
    img.src = catData.data.images.original.url;
  }
</script>

To use this function, we just simply need to call it with getCats() in our code.

<script>
  const img = document.querySelector('img');

  async function getCats() {
    const response = await fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'});
    const catData = await response.json();
    img.src = catData.data.images.original.url;
  }
  getCats();
</script>

This code will behave exactly like the code from the last lesson, it just looks a bit different after refactoring. async/await are very useful tools when it comes to cleaning up asynchronous javascript code. It is important to remember async/await are just promises written in a different way. Do the assignments below, and dive deeper into the understanding of async/await.

  1. Read this article for a solid introduction to async/await. this article also has some good examples of it’s use.

  2. Read this article for a more in-depth look at async/await, including how to handle errors.

  3. Watch the next video for a good overview on async/await and it’s purpose, along with a special trick.

Additional Resources

  1. This video is an example of how you can change callbacks, to promises, to async/await.

  1. This video gives a comprehensive view of Promises, async, and await.


Material based on Erik Trautman | The Odin Project

Feedback

  • Is there anything we can help with up to this point? Do you have something to suggest about this chapter? Let us know in the comments below.

UPDATED: 19.01.2021

Working with APIs

Introduction

One of the most powerful things a web developer can do is fetching data from a server and displaying it creatively on their site. In many cases, the server solely exists for that specific site. The server could contain blog posts, user data, high scores for a game or anything else. In other cases, the server is an open service that serves data to anyone that wants to use it (i.e. weather data or stock prices). In either case, the methods of accessing and then using that data are essentially the same.

APIs

Servers that are created for serving data for external use (in websites or apps) are often referred to as APIs or Application Programming Interfaces.

There are multiple ways of requesting data from an API, but all of them basically do the same thing. For the most part, APIs are accessed through URLs, and the specifics of how to query these URLs changes based on the specific service you are using. For example, the OpenWeatherMap API has several types of data that you can request. To get the current weather in a specific location, you need to request data from this URL:

api.openweathermap.org/data/2.5/weather?q=London,uk

You’ll want to switch out the city for the location you’re requesting. The specifics for using any API are usually documented on the service’s website. Check here for the OpenWeatherMap API documentation.

If you haven’t already, go ahead and paste the weather URL above into your browser…(we’ll wait).

Unless the implementation of that specific API has changed, you probably get an error like this:

{"code":401, "message": "Invalid API key. Please see http://openweathermap.org/faq#error401 for more info."}

This brings us to another point about APIs. In most cases, you have to sign up and get an API key to use them. Obtaining the API key is as simple as signing up on their website and using it is usually as easy as pasting it into the URL:

http://api.openweathermap.org/data/2.5/weather?q=London,uk&APPID=1111111111

(exactly how to include the key changes from service to service)

Services like the OpenWeatherMap use API keys to track who is requesting the data they serve, and how much data they are requesting. The reason they do this is so that people can’t take advantage of their service. Running servers, especially large ones costs money, and while each current weather request (or whatever) is relatively cheap, if the amount of requests gets too high the cost could be significant. Imagine using that API to create an amazing weather app that gets used all over the world….you could easily have thousands of people accessing that data every minute!

By signing up for a service and getting an API key you are letting the service track how much you are actually using. In many cases services are limited as to how much data they can request for free. With the weather app example, their free plan only allows you to make 60 requests per minute and also limits what types of data you can access (details here if you’re interested). So, if your app became successful, you would probably need to pay for a better account.

Luckily for us, the majority our apps are only going to be used by us and the people that view our portfolios. So we’ll get by just fine with free services.

Once you get a key (try this now if you like!) and waited for its activation (see Do I need to activate my API key?) you can paste the URL into the browser again (including your key of course) and hopefully, you’ll see a proper response:

{"coord":{"lon":-77.73,"lat":38.77},"weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"01d"}],"base":"stations","main":{"temp":75.74,"pressure":1017,"humidity":57,"temp_min":71.6,"temp_max":78.8},"visibility":16093,"wind":{"speed":3.87,"deg":291},"clouds":{"all":1},"dt":1504188900,"sys":{"type":1,"id":2886,"message":0.0053,"country":"US","sunrise":1504175992,"sunset":1504222878},"id":4775660,"name":"New Baltimore","cod":200}

Fetching Data

So how do we actually get the data from an API into our code?

A couple of years ago the main way to access API data in your code was using an XMLHttpRequest. This function still works in all browsers, but unfortunately, it is not particularly nice to use. The syntax looks something like this:

// Just getting XHR is a mess!
if (window.XMLHttpRequest) { // Mozilla, Safari, ...
  request = new XMLHttpRequest();
} else if (window.ActiveXObject) { // IE
  try {
    request = new ActiveXObject('Msxml2.XMLHTTP');
  }
  catch (e) {
    try {
      request = new ActiveXObject('Microsoft.XMLHTTP');
    }
    catch (e) {}
  }
}

// Open, send.
request.open('GET', 'https://url.com/some/url', true);
request.send(null);

Ouch. That was painful.

Developers, feeling the pain of having to write that stuff out, began writing 3rd party libraries to take care of this and make it much easier to use. Some of the more popular libraries are axios and superagent, both of which have their strengths and weaknesses.

More recently, however, web browsers have begun to implement a new native function for making HTTP requests, and that’s the one we’re going to use and stick with for now. Meet fetch:

// URL (required), options (optional)
fetch('https://url.com/some/url')
  .then(function(response) { 
    // Successful response :)
  })
  .catch(function(err) {
    // Error :(
  });

In case you’ve forgotten, scroll back up and look at how you would use XHR to do the same thing. While you’re admiring how nice and clean that code is, notice the .then() and .catch() functions there. Do you remember what those are? (PROMISES!)

Let’s change up our API for this example. We’re going to walk through an example using fetch with the giphy API to display a random gif on a webpage. The API requires you to sign up and get a free API key, so go ahead and do that here.

Giphy has several methods for searching and finding gifs which you can read about in their documentation. Today we’re just going to use the ‘translate’ endpoint because it’s the simplest one for our purposes. You can find the appropriate URL in their documentation by scrolling down here. What it tells us is that the correct URL is api.giphy.com/v1/gifs/translate and that it requires 2 parameters, your api_key and a search term. If you put it all together correctly (with YOUR API key) you should get something like this:

'https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats'
// of course we're searching for cats

Go ahead and try that URL (with YOUR API key) in a browser. If everything goes well you should get a relatively long string of data and no errors.

CORS

A side note before we start putting this into our code. For security reasons, by default, browsers restrict HTTP requests to outside sources (which is exactly what we’re trying to do here). There’s a very small amount of setup that we need to do to make fetching work. Learning about this is outside our scope right now, but if you want to learn a bit about it this wikipedia article is a decent starting point.

Whether or not you took the detour to learn all about Cross Origin Resource Sharing (CORS) the fix is simple. With fetch, you are able to easily supply a JavaScript object for options. It comes right after the URL as a second parameter to the fetch function:

fetch('url.url.com/api', {
  mode: 'cors'
});

Simply adding the {mode: 'cors'} after the URL, as shown above, will solve our problems for now. In the future, however, you may want to look further into the implications of this restriction.

Let’s Do This

For now, we’re going to keep all of this in a single HTML file. So go ahead and create one with a single blank image tag and an empty script tag in the body.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <img src="#" />
  <script>
  </script>
</body>
</html>

In the script tag, let’s start by selecting the image and assigning it to a variable so that we can change the URL once we’ve received it from the Giphy API.

<script>
  const img = document.querySelector('img');
</script>

Adding fetch with our URL from above is also relatively easy:

<script>
  const img = document.querySelector('img');
  fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'})
    .then(function(response) {
      console.log(response.json());
    });
</script>

You should now be able to open the HTML file in your browser, and while you won’t see anything on the page, you should have something logged in the console. The trickiest part of this whole process is deciphering how to get to the data you desire from the server’s response. In this case, inspecting the browser’s console will reveal that what’s being returned is another Promise… to get the data we need another .then() function.

<script>
  const img = document.querySelector('img');
  fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'})
    .then(function(response) {
      return response.json();
    })
    .then(function(response) {
      console.log(response);
    });
</script>

Now we have a JavaScript object and if you inspect it closely enough you’ll find that the data we need (an image URL) is nested rather deeply inside the object:

response

To get to the data we need to drill down through the layers of the object until we find what we want!

<script>
  const img = document.querySelector('img');
  fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'})
    .then(function(response) {
      return response.json();
    })
    .then(function(response) {
      console.log(response.data.images.original.url);
    });
</script>

Running the file should now log the URL of the image. All that’s left to do is set the source of the image that’s on the page to the URL we’ve just accessed:

<script>
  const img = document.querySelector('img');
  fetch('https://api.giphy.com/v1/gifs/translate?api_key=YOUR_KEY_HERE&s=cats', {mode: 'cors'})
    .then(function(response) {
      return response.json();
    })
    .then(function(response) {
      img.src = response.data.images.original.url;
    });
</script>

If all goes well, you should see a new image on the page every time you refresh!

If you’ve gotten lost along the way, the code below. Besides the glorious styling, this is what your version should look like.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <style>
    body {
      background-color: #e6d8e7;
      background-image: url("data:image/svg+xml,%3Csvg width='52' height='26' viewBox='0 0 52 26' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%239800a1' fill-opacity='0.22'%3E%3Cpath d='M10 10c0-2.21-1.79-4-4-4-3.314 0-6-2.686-6-6h2c0 2.21 1.79 4 4 4 3.314 0 6 2.686 6 6 0 2.21 1.79 4 4 4 3.314 0 6 2.686 6 6 0 2.21 1.79 4 4 4v2c-3.314 0-6-2.686-6-6 0-2.21-1.79-4-4-4-3.314 0-6-2.686-6-6zm25.464-1.95l8.486 8.486-1.414 1.414-8.486-8.486 1.414-1.414z' /%3E%3C/g%3E%3C/g%3E%3C/svg%3E");
      display: flex;
      height: 90vh;
      align-items: center;
      justify-content: center;
    }
  </style>
  <img src="#" alt="cat">
  <script>
  const img = document.querySelector('img')
  fetch('https://api.giphy.com/v1/gifs/translate?api_key=bb2006d9d3454578be1a99cfad65913d&s=cat', {mode: 'cors'})
    .then(function(response) {
      return response.json()
    })
    .then(function(response) {
      img.src = response.data.images.original.url
    })
    .catch(e => {
      console.log(e)
    })
</script>
</body>
</html>

Study

  1. Read the fetch documentation here. It’s not all that complicated to use, but we’ve only really scratched the surface at this point. You can also watch the last part of this live session which shows XHR and the Fetch API getting data from the Rest Countries JSON API.

  2. Check out this list of free, open APIs and let your imagination go wild.

  3. Expand on our little project here by adding a button that fetches a new image without refreshing the page.

  4. Add a search box so users can search for specific gifs. You should also investigate adding a .catch() to the end of the promise chain in case Giphy doesn’t find any gifs with the searched keyword. Add a default image, or an error message if the search fails.


Material based on Erik Trautman | The Odin Project

Feedback

  • Is there anything we can help with up to this point? Do you have something to suggest about this chapter? Let us know in the comments below.

UPDATED: 19.01.2021

Async

Introduction

Since JavaScript is the language of the web, there are some functions that by necessity are going to take a decent amount of time to complete, such as fetching data from a server to display on your site. For this reason, JavaScript includes support for asynchronous functions, or to put it another way, functions that can happen in the background while the rest of your code executes.

Learning Objectives

  1. What is a callback?
  2. What’s a promise?
  3. What are circumstances when promises are better than callbacks?
  4. What does the .then() function do?

Callbacks

In the recent past, the way that these were most commonly handled were with callbacks, and even now they are still used quite a lot in certain circumstances.

A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action. MDN

Callbacks are simply functions that get passed into other functions. For example:

myDiv.addEventListener("click", function(){
  // do something!
})

Here, the function addEventListener() takes a callback (the "do something" function) and then calls it when myDiv gets clicked.

You will likely recognize this pattern as something that happens all the time in JavaScript code. Unfortunately, though they are useful in situations like the above example, using callbacks can get out of hand, especially when you need to chain several of them together in a specific order. The rest of this lesson discusses patterns and functions that will help keep you out of Callback hell.

Take a moment to skim through this article before moving on. Or, if you prefer a video watch this.

Promises

There are multiple ways that you can handle asynchronous code in JavaScript, and they all have their use cases. Promises are one such mechanism, and they’re one you will see somewhat often when using other libraries or frameworks. Knowing what they are and how to use them is quite useful.

Essentially, a promise is an object that might produce a value at some point in the future. Here’s an example:

Lets say getData() is a function that fetches some data from a server and returns it as an object that we can use in our code:

const getData = function() {
  // go fetch data from some API...
  // clean it up a bit and return it as an object:
  return data
}

The issue with this example is that it takes some time to fetch the data, but unless we tell our code that, it assumes that everything in the function happens essentially instantly. So, if we try to do this:

const myData = getData()
const pieceOfData = myData['whatever']

We’re going to run into trouble because when we try to extract pieceOfData out of the returned data, the function getData() will most likely still be fetching, so myData will not be the expected data, but will be undefined. Sad.

We need some way to solve this problem, and tell our code to wait until the data is done fetching to continue. Promises solve this issue. We’ll leave learning the specific syntax for the articles you’re about to read, but essentially Promises allow you to do this:

const myData = getData() // if this is refactored to return a Promise...

myData.then(function(data){ // .then() tells it to wait until the promise is resolved
  const pieceOfData = data['whatever'] // and THEN run the function inside
})

Of course there many more occasions where one would want to use Promises beyond fetching data, so learning these things now will be very useful to you.

Study

  1. Read this article. It’s a good starting place and it’s short and to the point.

  2. Watch the next video. It’s a good place to get a feel for how one might actually use promises in the wild. Feel free to watch the other videos in the series, but they aren’t strictly needed at this point. The video also mentions the ES5/ES6 issue, don’t worry about that at this point either. All major browsers support Promises and we will teach you how to support older browsers in a later lesson.

  1. Watch this video to understand how asynchronous code works in JavaScript.

  1. Read Chapter 2: Callbacks and Chapter 3: Promises from You Don't Know JS. In Chapter 2, the author explains the problems with callbacks and why callback hell will be your worst enemy (hint: it’s the inversion of control and non-linear nature of callbacks). In Chapter 3, you go deep into the how and why of promises. This chapter is not the easiest read, but you’ll be a promise professional if you take the time to properly digest it. It’s worth the effort.

Additional Resources

  1. This is another useful article about Callback functions in JavaScript.

  2. The MDN Documentation for Promises. It might not be the best resource for learning all about them, but once you’ve read a more friendly article or tutorial, this will probably be the place you return to for a refresher.

  3. This video and this one too are both nice introductions to Promises if you need more repetition.

  4. This tutorial is another good introduction.


Material based on Erik Trautman | The Odin Project

Feedback

  • Is there anything we can help with up to this point? Do you have something to suggest about this chapter? Let us know in the comments below.

UPDATED: 13.01.2021

JSON

Introduction

JSON (JavaScript Object Notation) is a standardized format for structuring data. It is heavily based on the syntax for JavaScript objects. You will often encounter JSON formatted data when working with external servers or APIs – it is essentially the universal format for transmitting data on the web. Go through the following resources and you’ll be good to go.

Study

  1. This MDN tutorial is probably all you need…

  2. Read about the 2 JavaScript methods that you’ll most often be using when dealing with JSON – JSON.parse() and JSON.stringify().

  3. Mis-formatted JSON is a common cause of errors. This webpage lets you paste in JSON code and will search it for formatting errors.


Material based on Erik Trautman | The Odin Project

Feedback

  • Is there anything we can help with up to this point? Do you have something to suggest about this chapter? Let us know in the comments below.

UPDATED: 13.01.2021