JavaScript is a client-side scripting language or browser scripting. Client-side scripting language means that the browser will run these scripts. The opposite of the Client Side is the Server Side, the server side code of languages are run through web server.
* JavaScript is basically made up with 3 things.
1. ECMAScript (ES), This is the core functionality of JavaScript.
2. Document Object Model (DOM), It works with web page content.
3. Browser Object Model (BOM), It works with browsers.

JavaScript has a runtime model based on an event loop, which is responsible for executing the code, collecting and processing events, and executing queued sub-tasks. This model is quite different from models in other languages like C and Java.

Local Storage and Session Storage are relatively new APIs and are near identical with the sole exception of persistence.
Session Storage is only available for the duration of the browser session and is deleted when the tab or window is closed. Local Storage's data has to be deleted manually. And when you close the data browser or tab, the Session Storage becomes clear. Local Storage works for any tab, not for any specific tab.