JavaScript

JavaScript is the programming language of the web, enabling interactivity, logic, and dynamic behavior in browsers (and beyond, via Node.js). This chapter covers how JS code is ...

JavaScript has two categories of data types: primitive types (stored by value) and reference types (stored by reference). Understanding type coercion and equality checking is es...

Operators perform actions on values: arithmetic, comparison, logical, assignment, and more. ES6+ adds convenient operators like optional chaining and nullish coalescing.

Control structures direct the flow of execution — deciding which code runs and how many times, via conditionals and loops.

Functions are reusable blocks of logic. Modern JS adds arrow functions, default/rest parameters, and closures — a powerful mechanism where a function "remembers" variables from ...

Arrays store ordered lists of values. ES6+ provides powerful functional methods (map, filter, reduce) for transforming array data without manual loops.

Objects store data as key-value pairs and are the core building block for structuring complex data in JavaScript, alongside methods for creating, copying, and inspecting them.

Strings represent text. Modern JS provides template literals for readable string building plus a rich set of methods for searching, transforming, and splitting text.

The DOM (Document Object Model) is a live tree representation of an HTML page that JavaScript can read and modify — enabling dynamic content, styling, and structure changes with...

Events let JavaScript respond to user interactions (clicks, typing, scrolling) or browser actions (page load). Understanding event bubbling and delegation is key to writing effi...

JavaScript can read, validate, and react to form input values in real time — essential for interactive forms, live validation, and custom submit handling.

JavaScript is single-threaded but handles time-consuming tasks (network requests, timers) asynchronously via the event loop, Promises, and the more readable async/await syntax b...

JSON (JavaScript Object Notation) is a lightweight, text-based data format used to exchange data between a client and server. JS provides built-in methods to convert between JSO...

Error handling lets a program gracefully respond to unexpected failures — invalid input, failed network requests, or bugs — instead of crashing entirely. JavaScript uses try/cat...

ES Modules (ESM) let JavaScript code be split across multiple files, with explicit import/export statements controlling what's shared — improving organization, reusability, and ...

Browsers offer client-side storage APIs — localStorage and sessionStorage — to persist data without a server, useful for saving preferences, cached data, or session state.

Timers let JavaScript schedule code to run after a delay or repeatedly at intervals, powering things like debounced search, auto-save, slideshows, and countdowns.

ES6 classes provide a cleaner syntax for creating objects and implementing object-oriented patterns like inheritance and encapsulation, built on top of JavaScript's existing pro...