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Basic Frontend - Spring 2024

Lesson 16, Thursday, 2024-05-23

Lesson overview

  • Recap
  • Libraries
  • Libraries + fetch examples and tasks

Recap

  • JSON is a string representation of a JavaScript object
  • It stands for JavaScript Object Notation
  • JSON can be easily transferred (and stored)

Recap

async and await keywords in JavaScript provide a modern syntax to help us handle asynchronous operations.

async function fetchDataFromApi() {
  let res = await fetch('https://v2.jokeapi.dev/joke/Programming?type=single');
  let json = await res.json();
  console.log(json.joke);
}

Libraries

What is a library?

  • General definition: A collection of resources used for software development
  • More specifically, libraries usually relate to one specific type of functionality that you require for your app to function that (usually) someone else has written.
  • Examples: chart.js, d3.js, Plotly, Leaflet, ....

Loading a library

Up until now, this was our standard pattern:

<html>
  <body>
    Hello from HTML!
    <script>
      console.log('Hello from JavaScript!');
    </script>
  </body>
</html>

Javascript can also be loaded from a file inside the same directory as the HTML file:

<html>
  <body>
    <script src="main.js"></script>
  </body>
</html>

You can now write all your JavaScript in main.js.

Multiple scripts

We can add as many scripts as we want:

<html>
  <body>
    <script src="utilities.js"></script>
    <script src="recipes.js"></script>
    <script src="main.js"></script>
  </body>
</html>

This allows us to split long scripts into pieces

Multiple scripts

  • If we have multiple script tags, we can use all global variables and global functions from all scripts that are added before our script.
  • Scripts are run in order!
  • In the example on the last slide, recipes.js can use all globals from utilities.js, and main.js can use all globals from recipes.js and utilities.js

Scripts in header vs. body

We put our own scripts at the bottom of the <body> tag. This allows us to access all HTML elements via DOM API

We can put scripts also in the <head> tag. These are loaded before the page is rendered:

<html>
  <head>
    <script src="utilities.js"></script>
  </head>
  <body>
    <div id="myDiv">
      <!-- Elements go here -->
    </div>
    <script src="main.js"></script>
  </body>
</html>

Remote scripts

Scripts can also be remote addresses. In the example below, we load the plotly.js library:

<html>
  <head>
    <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
  </head>
</html>

Plotly

Plotly example

<html>
  <head>
    <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
  </head>
  <body>
    <div id="myGraph"></div>
    <script>
      let dataSet1 = {
        x: [1, 2, 3, 4],
        y: [0, 12, 8, 17],
        type: 'scatter',
      };
      Plotly.newPlot('myGraph', [dataSet1]);
    </script>
  </body>
</html>

Task 1

Here is an array of the temperature data for Berlin for 15th of November, 2023. Can you plot them using Plotly?

let temperatures = [
  9.9, 9.7, 9.6, 9.5, 9.6, 8.9, 7.9, 7.2, 7.5, 7.8, 7.9, 8.1,
  8.6, 8.6, 8.8, 8.4, 7.4, 6.5, 6.1, 6.0, 6.2, 6.3, 6.3
];

Bonus

Task 2

Create a new graph of the forecast of the new hourly temperature in Berlin for the next 3 days.

you can fetch the data by using the following URL

https://api.open-meteo.com/v1/forecast?latitude=52.50&longitude=13.48&hourly=temperature_2m&forecast_days=3

more information about the API: https://open-meteo.com/en/docs

Bonus

Let the user choose the number of days to be shown in the graph.