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Infosys · Typescript
Practice Typescript questions specifically asked in Infosys interviews – ideal for online test preparation, technical rounds and final HR discussions.
Questions
6
Tagged for this company + subject
Company
Infosys
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Subject
Typescript
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Go through each question and its explanation. Use this page for targeted revision just before your Infosys Typescript round.
Partial<T> flips every property in T to optional—perfect for patch/update payloads.
type User = { id: string; name: string };
type UserUpdate = Partial<User>; // { id?: string; name?: string }public (default) is visible everywhere, private is only inside the class, protected is inside the class and its subclasses, readonly prevents reassignment of that property after construction.
class User {
public id: string;
protected role: string = 'user';
private secret = 'shh';
readonly createdAt = new Date();
constructor(id: string){ this.id = id; }
}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 }Partial turns every property into an optional one. Handy for update DTOs and patch operations.
type User = { id: string; name: string };
type UserUpdate = Partial<User>; // { id?: string; name?: string }Use a colon after the variable name to add a type annotation. `let` is block-scoped and reassignable; `const` is block-scoped and not reassignable; `var` is function-scoped and generally avoided due to hoisting quirks.
let count: number = 0; const name: string = 'Ava'; var legacy: boolean = false; // function-scoped
Optional elements go after the element’s type using `?` inside the tuple type, e.g., `[A, B?]`. Standalone `[number?]` is not valid, and parentheses variants are not TypeScript syntax.
type MaybeLabel = [id: number, label?: string]; const a: MaybeLabel = [1]; const b: MaybeLabel = [2, 'two'];
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