An overview of JavaScript powered Web APIs that extend the functionality of the Web Browser

Curated by Kostas Minaidis | Updated: 04/07/2019


  • 01
    Media API Interact with Video & Audio Elements
  • 02
    Drag and Drop API All the Web's a Stage
  • 03
    Geolocation API Where in the World are we?


Media API

The HTML5 Media Elements

HTML5 can natively render video and audio in web pages using the <video> and <audio> HTML Media Elements.

Media Elements

The <audio> and <video> elements.

Let's add a video:

<video src="trailer.mp4"></video> <video src=""></video>

Let's add some music:

<audio src="mozart.mp3"></audio> <audio src=""></audio>

The <source>
Media Element

Providing multiple media sources for compatibility.

1) Opening <audio> tag

2) First audio source: mp3 file with appropriate MIME type attribute

"A media type (also known as a Multipurpose Internet Mail Extensions or MIME type) is a standard that indicates the nature and format of a document, file, or assortment of bytes."

3) Second audio source

4) Ready!

                                <audio controls>

                                    <source src="audio.mp3" type="audio/mp3">

                                    <source src="audio.ogg" type="audio/ogg">



Media API

Controlling Media Elements with JavaScript

The Media API allows you to interact with the Media Elements. It acts as a middleman, offering a set of commands for observing and controlling the Media elements.

Media API

Methods & Properties

Code Time!

( Class-Practice-01 )

1) Create an HTML page

2) Add a <video></video> element (Use this source)

2.1) Add a poster attribute. (Use this source)

3) Add a <script></script> tag just before the closing </body> tag

4) Use document.querySelector() to target the video element and store it in a variable named video

5) Use Media API methods

Methods:; video.pause(); Combine setTimeout and play/pause Combine the click event with play/pause

Challenge #1: apply background fade effect on play/pause

Challenge #2: Attach Play/Pause events directly on the video

Properties: ( Must be used with proper events )

video.duration; video.currentTime; // GET video.currentTime = 100; // SET

Full list of MediaElement Properties and Methods

Media API


Code Time!

( Class-Practice-02 )
canplay play pause ended loadeddata / loadedmetadata

Combine loadedmetadata event with duration property


Combine timeupdate event with currentTime property

Full list of MediaElement Events here and here.

References & Sources:


Drag & Drop API

Making draggable and droppable elements

Introduced with the HTML5 specification, the Drag and Drop API gives us the ability to drag elements from one place and drop them on other elements, much like our Operating Systems (Windows, Mac, Linux) and Desktop applications work.





Your imagination is the limit!

The Basics

1) Create some draggable elements (source)

2) Create some droppable elements (target)

3) Select a draggable element with a mouse

4) Drag the element to a droppable element and release the mouse button

The Code - 1/3

It's all about specifying draggable and droppable elements, and listening on Events.

1) Create a draggable Element and a drop target Element

2) Making an element draggable is as simple as setting the draggable attribute of an element to true

3) Setting an element as a drop target requires to disable the default dragover behavior.

3.1) Get the drop element.

3.2) Define a function that will prevent the default dragover behavior.

3.3) Handle the drop event.


                                <div id="draggable" draggable="true"> Draggable Element </div>

                                <div id="drop-target"> Drop Target </div>


                                let dropTarget = document.querySelector("#drop-target");

                                function handleDragOver( event ){ event.preventDefault(); }
                                dropTarget.addEventListener( "dragover",handleDragOver );

The Code - 2/3

A simple drag and drop communication requires the dragstart and drop events to be handled.

1) Store a reference of the draggable element in a variable

2) Handle the dragstart event of the draggable element

2) Handle the drop event of the drop element


                            // ...Code from Part 1/2
                            let draggable = document.querySelector("#draggable");

                            draggable.addEventListener( "dragstart", handleDragStart );

                            function handleDragStart(e){
                                console.log( e );

                            dropTarget.addEventListener( "drop", handleDrop );

                            function handleDrop(e){
                                console.log( e );


The DataTransfer Object

The DataTransfer object holds the data that is being dragged during a drag and drop operation.

It holds one or more data items, each of one or more data types.

In its simplest form, transfering data from a draggable element to a drop target is a 2-step process:

Step 1) Set data on dragstart event using event.dataTransfer.setData( format, data )

Step 2) Read data on drop event using event.dataTransfer.getData( format )

The Code - 3/3

1) Set some simple text data when the drag starts.

2) Access the data on the drop event.


                                // ...Code from Part 2/2
                                function handleDragStart(e){
                                    e.dataTransfer.setData( "text/plain", "Some data" );
                                function handleDrop(e){
                                    let data = e.dataTransfer.getData( "text/plain" );

Let's Code!

Let's build a Tasks Board


  • Application Planning
  • Boilerplate
  • Coding

In Progress


      Initial Souce Code


      1) Create a draggable element

      2) Listen on the dragstart event

      3) Set some transfer data

      4) Create a droppable element

      5) Prevent default behavior on the dragover
      event and listen on the drop event

      6) Get the transfer data


      Geolocation API

      Where in the World are we?

      An easy to use API for accessing the browser's location.

      For privacy reasons, the user is asked for permission to report location information.

      Geographical Coordinates

      A Primer on Latitude & Longitude

      "Cartographers and geographers trace horizontal and vertical lines called latitudes and longitudes across Earth's surface to locate points on the globe."

      "Together, they form the Earth’s geographical coordinates, and represent the angular distance of any location from the center of the Earth."

      [ Source ]

      The Code

      1) Define a callback function that will handle the successful Geolocation retrieval

      2) Define a callback function that will handle errors

      3) Check to see if our browser supports the Geolocation API

      4) Use the getCurrentPosition method to initiate the geolocation retrieval process

      Remember: getCurrentPosition() is an asynchronous function

      5) Handle browsers that do not support Geolocation


                                  function geoSuccess( position ){
                                      console.log( position );
                                  function geoError( error ){
                                      console.log( error.message );
                                  if ( navigator.geolocation ) {
                                      navigator.geolocation.getCurrentPosition( geoSuccess, geoError );
                                  } else {
                                      // Geolocation API Not Supported

      The Data
      & Error Objects

      geoSuccess( position ){ ... }

      geoError( error ){ ... }

      On Success

                                      position: Object {
                                          timestamp: [ date/time of the Response ],
                                          coords: {
                                              latitude: [ Latitude as decimal ],
                                              longitude: [ Longitude as decimal ],
                                              accuracy: [ Accuracy of position ],
                                              altitude: [ Altitude in meters above sea level ],
                                              speed: [ Speed in meters/second ],

      On Error

                                      error: Object {
                                          code: [ 1-3 ],
                                          message: [ String Error Description ]

      Let's Code!

      Display Browser's Geolocation on a Map

      Using Open Street Maps & OpenLayers

      OpenStreetMap (OSM):"A collaborative project to create a free editable map of the world. The data is free, and free of legal and technical restrictions."

      OpenLayers: "OpenLayers is a JavaScript library which implements an API for developing dynamic map widgets on the web."

      OpenLayers Quickstart

      Click, Copy & Paste!

      Notable method: watchPosition()


      1) Check if the Browser supports the Geolocation API

      2) Call the getCurrentPosition() method to asynchronously get the position data

      3) Handle errors

      4) Use the data accordingly


      Canvas API

      The Picasso in the Browser

      Where can it be used?




      The Basics

      1) Add a <canvas> element in the webpage

      2) Get access to the <canvas> drawing context (2D,3D)

      3) Use the context Object methods and properties to paint on the canvas

      The Code

      1) Place a <canvas> element in your webpage

      2) Get a reference to the canvas element via JavaScript

      3) Get a reference to the canvas 2D Context

      4) Start drawing using the 2D Context


                                          <canvas id="canvas" width="200" height="100"></canvas>


                                  const canvas = document.querySelector("#canvas");
                                  const context = canvas.getContext("2d");
                                  context.fillRect( 0, 0, 200, 100 );

      Our Drawing Tools

      2D Context Methods & Properties

      MDN Reference

      Let's Code!

      Jamaica, Jamaica!


      1) Place Canvas

      2) Get Context

      2) Start Drawing!

      References & Sources:


      Web Storage API

      Persistent Browser Data

      1) sessionStorage: Storage for each given origin available as long as the browser is open, including page reloads.

      2) localStorage: Just like sessionStorage, but persists when the browser is closed and reopened.

      Data gets cleared only through JavaScript. No expiration date.

      Data is never transferred to the Server

      The Code

      1) Check if localStorage is supported

      2) Store a key, value pair

      3) Retrieve a key value

      4) Get number of key/value pairs stored

      5) Get key value using index number

      6) Clear key/value pair

      7) Clear all key/value pairs

      8) Same rules apply for sessionStorage

      Storage data can also be accessed through the Browser's Developer Tools. On Chrome, go to: Developer Tools > Application > Storage > Local Storage


                                      if ( localStorage ){
                                          localStorage.setItem( key, value );
                                          localStorage.getItem( key );
                                          localStorage.key( index );
                                          localStorage.clearItem( key );
                                      if ( sessionStorage ){ 
                                          sessionStorage.setItem( key, value ); 

      Challenge #1

      Sources: [ Video | Poster Image ]

      1) Get video element

      2) Get Current Time element

      3) Make the <video> listen on the timeupdate event

      4) Get currentTime

      5) Set Current time element innerHTML

      6) Store currentTime in localStorage

      7) When page loads, get currentTime from localStorage

      8) Set currentTime

      Challenge: Create a Canvas arc that shows the video progress