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TypeScript 19 errors

TypeScript Errors

Assignability, missing declarations, strict null checks and generic constraints.

Understanding TypeScript errors

TypeScript errors are the compiler describing a mismatch between what you declared and what you did. Nearly all of them fall into assignability (this shape is not that shape), missing declarations (a JavaScript package with no types), or strict null checks (a value can be undefined on a path you did not handle). Casting with as or any silences the message without fixing the underlying mismatch, which usually reappears at runtime.

How to debug TypeScript errors

  1. Read the error from the innermost "Types of property X are incompatible" line outward. That nested line names the actual mismatch.
  2. For missing declarations, try npm i -D @types/<pkg> first; if none exists, write a minimal .d.ts rather than reaching for any.
  3. Narrow rather than assert. A type guard, an in check, or an early return preserves safety where as discards it.
  4. Use tsc --noEmit --pretty to check the whole project; editors sometimes use a different TypeScript version than the build.
  5. Check strict, skipLibCheck and moduleResolution in tsconfig when errors appear only in CI or only in the editor.

Tools worth reaching for

  • tsc --noEmit
  • ts-node / tsx
  • @types/* packages
  • typescript-eslint
  • editor TS version selector

All 19 TypeScript errors

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