Get the Preplance app for a seamless learning experience. Practice offline, get daily streaks, and stay ahead with real-time interview updates.
Get it on
Google Play
4.9/5 Rating on Store
Typescript · Question Set
Modules & Build interview questions for placements and exams.
Questions
12
Included in this set
Subject
Typescript
Explore more sets
Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for Typescript.
When enabled, you can write `import x from 'cjs-lib'` for CommonJS modules that export with `module.exports`. It smooths default import ergonomics.
// tsconfig.json
{
"compilerOptions": {
"esModuleInterop": true
}
}
// Now possible:
import express from 'express';For complete preparation, combine this set with full subject-wise practice for Typescript. You can also explore other subjects and sets from the links below.
Setting `"strict": true` enables a bundle of strictness flags (like `noImplicitAny`, `strictNullChecks`) that catch bugs early.
// tsconfig.json
{
"compilerOptions": {
"strict": true
}
}Set `baseUrl` (the root) and define `paths` mappings. This shortens import paths and avoids deep relative imports.
// tsconfig.json
{
"compilerOptions": {
"baseUrl": ".",
"paths": { "@app/*": ["src/*"] }
}
}
// import { util } from '@app/utils/util';Split your code into buildable subprojects. Turn on `composite` and reference projects so TS can reuse build info and type check faster.
// packages/a/tsconfig.json
{
"compilerOptions": { "composite": true, "outDir": "dist" },
"include": ["src"]
}
// root tsconfig: {
// "references": [{ "path": "packages/a" }, { "path": "packages/b" }]
// }First look for community typings on DefinitelyTyped (`@types/...`). If none exist, write your own `.d.ts` declaration file for the library.
// Install typings:
// npm i -D @types/lodash
// Or create: types/my-lib/index.d.ts
declare module 'my-lib' { export function doThing(): void }`unknown` forces you to check and narrow before using the error value. It avoids the unsafe, anything-goes behavior of `any`.
try {
// ...
} catch (e: unknown) {
if (e instanceof Error) console.error(e.message);
else console.error('Unknown error');
}Use ES modules (`import`/`export`) for clear boundaries, tree-shaking, and compatibility with modern bundlers and runtimes. Namespaces and globals are legacy patterns and make code harder to split.
// math.ts
export const add = (a: number, b: number) => a + b;
// app.ts
import { add } from './math.js';
console.log(add(2,3));You can reopen a module’s declaration in a `.d.ts` file and add missing types or members. This is great for patching third-party typings without editing `node_modules`.
/* types/lib-augment.d.ts */
declare module 'some-lib' {
export function fancy(): string;
}Module resolution decides how an import path maps to a file. In Node-style resolution, TS looks for exact files, then index files, then `node_modules`. Use path mapping to replace long `../../..` with friendly aliases and to swap mocks in tests. Keep aliases aligned with your bundler (Vite/Webpack) and your runtime (Node or browser).
// tsconfig.json
{
"compilerOptions": {
"baseUrl": ".",
"paths": { "@app/*": ["src/*"], "@tests/*": ["tests/*"] }
}
}
// Import now: import { foo } from '@app/utils/foo';Project references split a large codebase into smaller TS projects that know about each other. Each subproject sets `composite: true`. Benefits: faster incremental builds, isolated outputs per package, and better IDE responsiveness. The root config lists references so `tsc -b` can build in the right order. CI becomes more stable and local feedback is quicker.
// root/tsconfig.json
{
"files": [],
"references": [
{ "path": "packages/core" },
{ "path": "packages/web" }
]
}
// packages/core/tsconfig.json
{
"compilerOptions": { "composite": true, "outDir": "dist" },
"include": ["src"]
}
// Build all
// npx tsc -bNode app: target a modern Node version, keep ESM/CJS consistent, emit source maps, and enable strict checks. React app: target modern browsers, use JSX transform, and enable strict to catch UI bugs early. Quick Node example: strict, module: node16 or nodenext, target: ES2021+, moduleResolution: node, esModuleInterop: true, outDir: dist, sourceMap: true, noEmitOnError: true. Quick React example: strict, jsx: react-jsx, target: ES2020+, module: ESNext, moduleResolution: bundler or node, paths for aliases, skipLibCheck for CI speed if needed (but keep it on locally if possible).
// Node tsconfig.json
{
"compilerOptions": {
"strict": true,
"target": "ES2021",
"module": "NodeNext",
"moduleResolution": "NodeNext",
"esModuleInterop": true,
"outDir": "dist",
"sourceMap": true,
"noEmitOnError": true
},
"include": ["src"]
}
// React tsconfig.json
{
"compilerOptions": {
"strict": true,
"target": "ES2020",
"module": "ESNext",
"moduleResolution": "Bundler",
"jsx": "react-jsx",
"baseUrl": ".",
"paths": { "@/*": ["src/*"] }
}
}Create a `.d.ts` in your `types/` folder, reopen the module with `declare module`, and add the new types. Keep all patches in one place so upgrades are safe and your codebase stays clean.
/* types/express-augment.d.ts */
declare module 'express' {
interface Request {
userId?: string;
}
}
// usage in app code
import express from 'express';
const app = express();
app.use((req, _res, next) => { req.userId = 'u1'; next(); });