I thought this list was interesting (from ‘How hard is to learn Javascript’)
- Add new HTML to a webpage, change the existing content, and modify styles of the webpage content.
- React to user actions such as mouse click response, pointer movements, and key presses.
- Download and upload files, and send requests over the network to remote servers.
- Receive and set cookies from web pages, question users about them, and show them notifications.
- Save web data on the local or client-side storage.
- Make websites more interactive, at least more than a static page of text.
- Develop mobile applications that you have on your phone as well as tablet.
- Create web browser-based games, the ones you play directly from your web browser.
- Although JavaScript is used mainly for front-end development, it’s still versatile enough to handle back-end infrastructure as well.
And the article went on to say:
All these uses mean that using JavaScript has the following merits:
- Less Server Interaction − Before sending the page to the server, JavaScript lets you validate the user input. This results in minimizing server traffic, which ultimately means a- minimum load on your server.
- Immediate Feedback To The Visitors – As the feedback is prompt, the website visitors don’t have to wait for a page to reload to realize if they have missed entering some data.
- Increased Interactivity − You can increase the interactivity of your website by adding interfaces that react when a user moves over them with a mouse or initiates them via a keyboard.
- Richer Interfaces − To provide a rich quality interface to your site visitors, you can use JavaScript and include items like drag-and-drop components and sliders.