Legacy-to-TypeScript: 5 Copy-Paste Refactor Patterns
Stop rewriting the same TypeScript fixes. Get before/after code patterns for CommonJS conversion, type elimination, callbacks, dynamic imports, and DOM typing, the five blockers that slow every migration.
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What's Inside
- CommonJS → ESM Module Conversion Patterns
- Eliminating `any` Types in Legacy Data Flows
- Callback-Heavy Code → Async/Await Refactor Templates
- Dynamic Require() Strategies (Imports, Lazy-Loading)
- Typing Legacy DOM Manipulation & jQuery Patterns
Pattern 1: CommonJS → ESM Module Conversion Change `module.exports = { function1, function2 }` to `export { function1, function2 }`. Change `const x = require('./module')` to `import x from './module'`. When the CommonJS file exports a single default, use: `export default function1` instead of `module.exports = function1`. --- Pattern 2: Incremental Type Extraction Don't type the entire flow. Start at the leaf functions (the ones that actually use the data), then work backwards. Step 1: Identify where data is actually used. Example: if a function calls `.toUpperCase()`, type that parameter as `string`. Step 2: Create an interface for data that enters your system from external sources (API responses, file reads).
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