1.2 JavaScript

5 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
• 0021 Read and write files in Node.js with fs/promises A complete Node script that walks a folder, reads text files, and writes a JSON report safely, showing the everyday fs/promises calls… Beginner · How-to · Any system Script Node.js 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