1.2 JavaScript
Every entry filed under JavaScript and its subtopics.
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- You are new to this topic.
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- You use it, and want to get better.
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- You know it well and need the details.
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- Build something small from start to finish, step by step.
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- Fixes an error
- An error message, what it means, and how to solve it.
20 entries match these filters
- 0386 Install Node.js on Linux, macOS and Windows Get Node.js and npm on any desktop OS. Use a version manager (nvm or fnm) when you work on several projects, or… Beginner · Step by step · Linux, macOS, Windows Article Installing languages & tools · Node.js 15 Oct 2026
- 0320 Fix: address already in use (EADDRINUSE) Something is already listening on the port your program wants. Find the process with lsof or ss, stop it or pick another… Beginner · Fixes an error · Linux, macOS Article Networking & firewalls · Node.js · Processes & ports 15 Oct 2026
- 0319 Fix: npm ERR! EACCES permission denied npm cannot write to a directory it needs: the global install location, its cache in ~/.npm, or a node_modules owned by root.… Beginner · Fixes an error · Linux, macOS Article Common errors · Node.js 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 · Guided project · Any system Article Making requests · Node.js · Status codes 15 Oct 2026
- 0085 fetch with timeout, retries, and exponential backoff A drop-in fetch wrapper that times out slow requests, retries network errors and 429/5xx responses with jittered exponential backoff, and honors Retry-After. Advanced · Step by step · Any system, Browser Script Async code · Making requests 15 Oct 2026
- 0097 Express (expressjs/express) A minimal and flexible web framework for Node.js, built around routes and middleware, and the foundation of countless APIs and other frameworks. Any system Repo Node.js · Web frameworks 15 Oct 2026
- 0023 Run async tasks with a concurrency limit A small mapLimit helper that runs an async function over many items with at most N in flight, keeps result order, stops… Advanced · Step by step · Any system Script Async code 15 Oct 2026
- 0030 Axios A promise-based HTTP client for browsers and Node.js with interceptors, automatic JSON handling, request cancellation and a consistent API in both environments. Any system Repo Async code · Making requests 15 Oct 2026
- 0020 Debounce and throttle functions in plain JavaScript Two small dependency-free helpers that limit how often a function runs: debounce waits for a pause, throttle runs at most once per… Intermediate · Step by step · Any system Script Patterns 15 Oct 2026
- 0031 Lodash A JavaScript utility library with helpers for arrays, objects, strings and functions, including debounce, throttle, deep cloning and safe property access. Any system Repo Patterns 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 · Step by step · Any system Script Node.js 15 Oct 2026
- 0022 Build a small Node.js CLI with util.parseArgs A complete, dependency-free command-line tool in Node: options and flags with parseArgs, input from files or a pipe, help text, and meaningful… Intermediate · Step by step · Any system Script Node.js 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 · Fixes an error · Any system Article Common errors · Node.js 15 Oct 2026
- 0028 Node.js The source of the Node.js runtime: a JavaScript engine (V8) plus APIs for files, networking, processes and more, used to run JavaScript… Linux, macOS, Windows Repo Node.js 15 Oct 2026
- 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 · Explains an idea · 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 · Cheat sheet · Any system Article Basics 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 · Cheat sheet · 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 · Fixes an error · Any system Article Basics · Common errors 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 · Explains an idea · Any system Article Async code 15 Oct 2026
- 0019 fetch with timeout, retries and proper error handling A reusable fetchJson helper for Node 20+ and browsers that adds a timeout, retries with backoff for temporary failures, and clear errors… Intermediate · Step by step · Any system Script Async code · Making requests 15 Oct 2026