1.2 JavaScript

9 entries match these filters

• 0016 let, const and var: variables and scope in JavaScript Use const by default, let when a value must change, and avoid var. The difference is about scope: where a variable is… Beginner · Concept · Any system Article Basics 15 Oct 2026
• 0017 JavaScript array methods cheat sheet: map, filter, reduce and friends A quick reference for the array methods you use every day, with what each one returns and whether it changes the original… Beginner · Reference · Any system Article Basics 15 Oct 2026
• 0018 Promises and async/await explained A promise is a placeholder for a value that arrives later. async/await lets you write code that waits for promises as if… Intermediate · Concept · Any system Article Async code 15 Oct 2026
• 0025 Regular expressions cheat sheet (JavaScript flavor) The regex syntax you actually use, from character classes and quantifiers to groups, lookarounds and flags, with the JavaScript methods that apply… Beginner · Reference · Any system Article Basics · Basics 15 Oct 2026
• 0026 Fix: TypeError: Cannot read properties of undefined (reading ‘x’) You tried to read a property from a value that is undefined or null. Find which value is missing, then guard it… Beginner · Fix · Any system Article Basics · Common errors 15 Oct 2026
• 0027 Fix: SyntaxError: Cannot use import statement outside a module The file uses ES module import syntax, but Node or the browser is loading it as a classic script or CommonJS. Tell… Intermediate · Fix · Any system Article Common errors · Node.js 15 Oct 2026
• 0087 CORS explained: why the browser blocks your request CORS is the browser rule that decides whether JavaScript on one origin may read a response from another. The server opts in… Intermediate · Concept · Browser Article Async code · Making requests 15 Oct 2026
• 0088 Fix: Access to fetch at ‘…’ from origin ‘…’ has been blocked by CORS policy The browser refused to give your script a cross-origin response because the server did not send the right Access-Control-* headers. Fix it… Intermediate · Fix · Browser Article Common errors · Making requests 15 Oct 2026
• 0263 Build a notes REST API with plain Node.js: CRUD, validation, status codes and CORS Write a small JSON API for notes using only Node.js built-ins: create, read, update and delete, input validation, correct HTTP status codes,… Intermediate · Tutorial · Any system Article Making requests · Node.js · Status codes 15 Oct 2026