Fix: npm ERR! Missing script: "start"
How to fix "npm ERR! Missing script" for start, dev, build, and test. Covers adding scripts to package.json, common framework configurations for React, Next.js, Vite, Angular, Express, and Nest.js.
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Fix: React Hook "useXxx" is called conditionally. React Hooks must be called in the exact same order in every component render.
How to fix 'React Hook is called conditionally', 'Rendered more hooks than during the previous render', 'Invalid hook call', and other React Hooks order errors. Covers conditional hooks, hooks in loops, hooks after early returns, duplicate React versions, and ESLint setup.
Fix: ModuleNotFoundError: No module named in Python
How to fix 'ModuleNotFoundError: No module named' and 'ImportError: No module named' in Python. Covers pip install, pip vs pip3, virtual environments, package name vs import name mismatches, PYTHONPATH, and IDE interpreter issues.
Fix: process.env.VARIABLE_NAME Is Undefined (Node.js, React, Next.js, Vite)
How to fix 'process.env.VARIABLE_NAME is undefined' and environment variables not loading from .env files in Node.js, React, Next.js, Vite, and Docker.
Fix: Port 3000 Is Already in Use (EADDRINUSE)
How to fix 'port 3000 is already in use', 'EADDRINUSE', and 'address already in use :::3000' errors in Node.js, React, Next.js, and other frameworks on macOS, Linux, and Windows.
Fix: npm ERR! ERESOLVE unable to resolve dependency tree
How to fix the ERESOLVE unable to resolve dependency tree error in npm. Covers root causes, peer dependency conflicts, --legacy-peer-deps, --force, npm overrides, and edge cases with React 18, TypeScript, and monorepos.
Fix: Permission denied (publickey) – Git SSH Authentication Failed
How to fix 'git@github.com: Permission denied (publickey)' and 'fatal: Could not read from remote repository' when pushing or cloning over SSH. Covers key generation, ssh-agent, GitHub/GitLab setup, and edge cases.
Fix: TypeError: Cannot read properties of undefined (reading 'xxx')
How to fix 'TypeError: Cannot read properties of undefined', 'Cannot read property of undefined', and 'Cannot read properties of null' in JavaScript, TypeScript, and React. Covers optional chaining, async data fetching, destructuring, and nested object access.
Fix: EACCES permission denied when installing npm packages globally
How to fix 'Error: EACCES: permission denied, access /usr/local/lib/node_modules' when running npm install -g on macOS or Linux. Multiple solutions ranked by recommendation.
Fix: Error Cannot find module in Node.js (MODULE_NOT_FOUND)
How to fix 'Error: Cannot find module' and 'MODULE_NOT_FOUND' in Node.js. Covers missing packages, wrong import paths, node_modules issues, TypeScript moduleResolution, ESM vs CJS, and monorepo hoisting.
Fix: git push rejected – non-fast-forward error
How to fix 'error: failed to push some refs' and '! [rejected] main -> main (non-fast-forward)' in Git. Covers pull, rebase, force push, and edge cases.
Fix: Access to fetch has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header
How to fix 'Access to fetch at ... from origin ... has been blocked by CORS policy: No Access-Control-Allow-Origin header is present on the requested resource' in JavaScript. Covers Express, Django, Flask, Spring Boot, ASP.NET, nginx, Apache, dev proxies, preflight requests, credentials, and edge cases.