JavaScript

The language that powers the web

JavaScript makes pages interactive and runs entire applications. Variables, functions, arrays and objects, then the DOM, asynchronous code, closures and modern tooling: the backbone of every web developer.

Foundations

Beginner - the basics, step by step

• Variables (let, const) and primitive typesDiscover how to store information with let and const, and identify the basic value types in JavaScript.
• Operators and conditions (if/else, comparisons, ===)Learn how to calculate, compare values with === and make your program take decisions with if and else.
• Loops: for, while, for...ofRepeat instructions without repeating yourself thanks to for, while and for...of loops.
• Functions: declaration, parameters, returnCreate reusable blocks of code with function, pass them parameters and get their results back with return.
• Arrays and objects: creating, reading, modifyingStore several values in arrays, describe entities with objects, then learn how to read and modify them.

Progression

Intermediate - build real things

• Array methods: map, filter, reduce, findLearn to transform, filter, and aggregate data with the four array methods most used in real-world projects.
• Arrow functions, scope, and template literalsMaster arrow syntax, block scope, and closures, then build dynamic strings with template literals.
• Destructuring and spread/restCleanly extract data from objects and arrays, then copy and merge structures with the spread operator.
• Manipulating the DOM: querySelector, event listenersSelect elements on the page, react to clicks, and adopt event delegation for performant code.
• JSON, localStorage, and your first fetchSerialize your data as JSON, persist it in the browser with localStorage, and retrieve remote data with fetch.

Advanced

Proficient - advanced patterns and performance

• Closures and lexical scopeMaster how closures capture variables so you can encapsulate state and avoid scoping pitfalls.
• this, prototypes and classesUnderstand how this is resolved dynamically, how the prototype chain works, and what classes actually add to the object model.
• Async in depth: promises, async/await, error handlingLeverage the event loop, parallelize your promises correctly, and make asynchronous error handling reliable.
• ES modules: import/export, structuring a projectStructure your projects with ES modules by leveraging their static analysis and avoiding toxic barrels and circular dependencies.
• Debugging and robustness: try/catch, advanced console, custom errorsBuild an explicit error strategy with dedicated classes, well-placed catch boundaries, and a console used to its full potential.

Mastery

Expert - architecture, internals and edge cases

• The event loop: call stack, microtasks, macrotasksUnderstand how the engine actually schedules synchronous code, microtasks, and macrotasks.
• Iterators, generators, and iteration protocolsMaster the protocols behind for...of, spread, and destructuring, then use generators to produce lazy sequences.
• Proxy, Reflect, and metaprogrammingIntercept the language's fundamental operations with Proxy traps and cleanly delegate default behavior with Reflect.
• Memory and performance: GC, WeakMap/WeakRef, debounce/throttleUnderstand how the garbage collector works, use weak references to avoid leaks, and smooth out expensive work with debounce and throttle.
• Functional patterns: currying, composition, immutabilityStructure your code with currying, function composition, and immutable data to gain predictability and testability.