TypeScript Project Planning & Execution 3 — Questions and Answers
Question 1: Which tool is commonly used to enforce consistent TypeScript code style and catch common bugs beyond what the compiler checks?
- Prettier
- ESLint with @typescript-eslint (Correct answer)
- Babel
- ts-node
Correct answer: ESLint with @typescript-eslint
The `@typescript-eslint` plugin extends ESLint with TypeScript-aware rules for linting patterns the compiler doesn't flag.
Question 2: In a TypeScript project, what is the purpose of a `.d.ts` declaration file?
- To run TypeScript code directly without compilation
- To provide type information for JavaScript libraries without source code (Correct answer)
- To configure the TypeScript compiler options
- To define environment variables for the build
Correct answer: To provide type information for JavaScript libraries without source code
Declaration files (`.d.ts`) expose type definitions for libraries so TypeScript consumers get autocomplete and type safety.
Question 3: Your team uses `strict: true` in tsconfig. Which individual flag does this NOT enable?
- strictNullChecks
- noImplicitAny
- noUnusedLocals (Correct answer)
- strictFunctionTypes
Correct answer: noUnusedLocals
`noUnusedLocals` is a separate flag not included in `strict: true`; it must be opted into independently.
Question 4: Which approach correctly types a React component's props in a TypeScript project to enforce required vs optional fields?
- Use a plain JavaScript object with default values
- Define an interface with optional properties using `?` and required ones without (Correct answer)
- Use `PropTypes` from the react package
- Pass `any` type to avoid type errors
Correct answer: Define an interface with optional properties using `?` and required ones without
TypeScript interfaces with `?` for optional properties and required fields without it give components precise type safety.
Question 5: What does enabling `isolatedModules: true` in tsconfig prevent, and why is it important for tools like Babel?
- It prevents circular imports between modules
- It disallows const enums and namespace imports that require full-program analysis (Correct answer)
- It blocks dynamic imports in the codebase
- It enforces a single entry point per project
Correct answer: It disallows const enums and namespace imports that require full-program analysis
`isolatedModules` disallows TypeScript features that Babel (which transpiles file-by-file) cannot handle without full-program context.
Question 6: A TypeScript project's build is slow. Which tsconfig option enables TypeScript to reuse information from previous compilations to speed up incremental builds?
- skipLibCheck: true
- incremental: true (Correct answer)
- noEmit: true
- composite: true
Correct answer: incremental: true
`incremental: true` saves a build info file (`.tsbuildinfo`) so TypeScript only recompiles changed files on subsequent builds.
Question 7: Which npm script pattern is best practice for running type checking and tests in parallel in a TypeScript project's CI pipeline?
- "ci": "tsc --noEmit && jest"
- "ci": "tsc --noEmit & jest"
- "ci": "npm-run-all --parallel typecheck test" (Correct answer)
- "ci": "jest --typescript"
Correct answer: "ci": "npm-run-all --parallel typecheck test"
`npm-run-all --parallel` runs multiple npm scripts concurrently, reducing total CI time compared to sequential execution.
TypeScript Project Planning & Execution 3
Which tool is commonly used to enforce consistent TypeScript code style and catch common bugs beyond what the compiler checks?