Fix: ESLint Parsing error: Unexpected token (JSX, TypeScript, ES modules)
How to fix ESLint 'Parsing error: Unexpected token' for JSX, TypeScript, and ES module syntax by configuring the correct parser, parserOptions, and ESLint config format.
Tag: javascript
17 articles
Fix: CORS preflight request blocked — Response to preflight does not have HTTP ok status
How to fix 'Response to preflight request doesn't pass access control check' and 'preflight channel did not succeed' CORS errors by handling OPTIONS requests, setting correct headers, and configuring your server.
Fix: Module parse failed: Unexpected token (Webpack / Vite / esbuild)
How to fix 'Module parse failed: Unexpected token' in Webpack, Vite, and esbuild by configuring the correct loaders and transforms for JSX, TypeScript, CSS, JSON, and other file types.
Fix: Hydration failed because the initial UI does not match what was rendered on the server (Next.js)
How to fix the Next.js hydration mismatch error. Covers invalid HTML nesting, browser extensions, Date/time differences, useEffect for client-only code, dynamic imports, suppressHydrationWarning, localStorage, third-party scripts, Math.random, auth state, and React portals.
Fix: TS2322 Type 'X' is not assignable to type 'Y'
How to fix TypeScript error TS2322 'Type is not assignable to type'. Covers literal types vs general types, string vs String, union types, interface compatibility, generic constraints, readonly arrays, excess property checking, discriminated unions, type assertions, type widening and narrowing, React event handlers, Promise return types, and enum mismatches.
Fix: SyntaxError: Unexpected token < in JSON at position 0
How to fix 'Unexpected token in JSON at position 0', 'JSON.parse: unexpected character', and 'Unexpected end of JSON input' in JavaScript and TypeScript. Covers API returning HTML instead of JSON, Content-Type mismatches, fetch URL typos, invalid JSON syntax, BOM characters, CORS proxies, and debugging with response.text().
Fix: Loading chunk failed / ChunkLoadError
How to fix 'Loading chunk failed', 'ChunkLoadError', and 'Failed to fetch dynamically imported module' in webpack, Next.js, React, and Vite. Covers stale deployments, CDN caching, publicPath misconfiguration, service worker cache, code splitting, dynamic import retry strategies, React.lazy error boundaries, and Next.js-specific solutions.
Fix: TS2532 Object is possibly 'undefined' / Object is possibly 'null'
How to fix TypeScript errors TS2532 'Object is possibly undefined', TS18048 'Object is possibly undefined', and 'Object is possibly null'. Covers optional chaining, nullish coalescing, type narrowing, non-null assertion, type guards, strictNullChecks, Array.find, Map.get, React useRef, and more.
Fix: Too many re-renders. React limits the number of renders to prevent an infinite loop.
How to fix 'Too many re-renders' in React. Covers calling functions in JSX instead of passing references, setState in the render body, useEffect infinite loops, object/array dependency issues, and how to debug re-renders with React DevTools.
Fix: Module not found: Can't resolve / Cannot find module or its corresponding type declarations
How to fix 'Module not found: Can't resolve' in webpack, Vite, and React, and 'Cannot find module or its corresponding type declarations' in TypeScript. Covers missing packages, wrong import paths, case sensitivity, path aliases, node_modules corruption, monorepo hoisting, barrel files, and asset imports.
Fix: [vite] Internal server error: Failed to resolve import
How to fix Vite's 'Failed to resolve import' error, including 'Does the file exist?', 'Optimized dependency needs to be force included', 'Pre-transform error', and '504 (Outdated Optimize Dep)'. Covers missing packages, path aliases, optimizeDeps, cache clearing, and CJS/monorepo edge cases.
Fix: Hydration failed because the initial UI does not match what was rendered on the server
How to fix Next.js and React hydration errors including 'Text content does not match server-rendered HTML', 'Expected server HTML to contain a matching <div> in <div>', and 'There was an error while hydrating'. Covers browser extensions, Date/time mismatches, invalid HTML nesting, window checks, localStorage, and third-party components.
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: 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: 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: 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: 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.