TypeScript Answers

Basic TypeScript Answers

#	Question	Answer	Examples
1	What is TypeScript?	A superset of JavaScript that adds static typing	It compiles down to plain JavaScript
2	Why use TypeScript?	Improves code maintainability, catches errors early, provides better tooling	Type checking during development, better code readability, autocompletion
3	What is static typing?	Checking variable types at compile time (before the code runs)	let name: string = "Alice";, let age: number = 30;
4	How do you declare a variable with a type?	Using a colon (:) followed by the type name	let isActive: boolean = true;
5	What are basic primitive types?	string, number, boolean, null, undefined, symbol, bigint	let message: string = "Hello";, let count: number = 100;
6	How do you define an array type?	Using Type[] or Array	let names: string[] = ["Bob", "Charlie"];, let numbers: Array = [1, 2, 3];
7	How do you define an object type?	Using an interface or type alias	interface User { name: string; age: number; } let user: User = { name: "Dave", age: 40 };
8	What is an interface?	Defines the shape of an object	interface Point { x: number; y: number; }
9	How do you define a function type?	Specifying types for parameters and the return value	function add(a: number, b: number): number { return a + b; }
10	What is the any type?	Allows a variable to hold a value of any type (use sparingly)	let data: any = "anything"; data = 123;
11	What is the void type?	Indicates a function does not explicitly return a value	function logMessage(): void { console.log("Logged"); }
12	What is the unknown type?	Similar to any, but requires type checking before use	let value: unknown = "test"; if (typeof value === 'string') { console.log(value.toUpperCase()); }
13	What is a union type ( | )?	Allows a variable to hold a value of several different types	let id: string | number = "abc"; id = 123;
14	What is an intersection type (&)?	Combines multiple types into a single type	type Person = { name: string }; type Employee = { id: number }; type FullTime = Person & Employee;
15	How do you compile TypeScript code?	Using the tsc command (TypeScript Compiler)	tsc myFile.ts

Intermediate TypeScript Answers

#	Question	Answer	Examples
1	Explain the difference between interface and type.	interface is primarily for object shapes; type can define object shapes, unions, primitives, etc.	interface User { name: string; }, type Point = { x: number; }, `type ID = string
2	What are Generics?	Allow you to write components that can work with a variety of types without losing type safety	function identity(arg: T): T { return arg; }, let output = identity("myString");
3	What is an Enum?	Defines a set of named constants	enum Color { Red, Green, Blue } let myColor: Color = Color.Green;
4	What is a Tuple?	An array with a fixed number of elements and known types for each element	let coordinate: [number, number] = [10, 20];
5	What is a Class in TypeScript?	A blueprint for creating objects with properties and methods	class Dog { name: string; constructor(name: string) { this.name = name; } bark() { console.log("Woof!"); } }
6	What are access modifiers (public, private, protected)?	Control the visibility of class members	class Animal { public name: string; private secret: string; protected species: string = "unknown"; }
7	What is inheritance in TypeScript?	Allows a class to inherit properties and methods from another class (extends)	class Cat extends Animal { meow() { console.log("Meow!"); } }
8	What is an abstract class?	A class that cannot be instantiated directly, serves as a base for other classes	abstract class Shape { abstract draw(): void; } class Circle extends Shape { draw() { console.log("Drawing Circle"); } }
9	What is a Type Assertion?	Tells TypeScript to treat a value as a specific type (use with caution)	let myInput = document.getElementById("myInput") as HTMLInputElement;
10	What is a Type Guard?	Used to narrow down the type of a variable at runtime	function processValue(value: string | number) { if (typeof value === 'string') { console.log(value.toUpperCase()); } }
11	How do you make a property optional in an object interface/type?	Using a question mark (?) after the property name	interface Config { url: string; timeout?: number; }
12	What is the readonly modifier?	Prevents a property from being reassigned after initialization	class Point { readonly x: number; constructor(x: number) { this.x = x; } }
13	What is a Type Alias?	Creates a new name for an existing type	type Coordinates = { x: number; y: number; }; let point: Coordinates = { x: 10, y: 20 };
14	What is a literal type?	Defines a type based on a specific literal value (string, number, boolean)	type Status = "pending" | "processing" | "completed"; let status: Status = "pending";
15	What are utility types?	Built-in types for common type transformations (e.g., Partial, Required, Pick, Omit)	let partialUser: Partial = { name: "Jane" };

Advanced TypeScript Answers

#	Question	Answer	Examples
1	Explain Decorators.	A way to add metadata or behavior to classes, methods, properties, or parameters	@Component({}) class MyClass { ... }, @logMethod() function myMethod() { ... }
2	What are Conditional Types?	Allows you to create a type based on a condition (similar to a ternary operator)	type IsString = T extends string ? true : false; let isStr: IsString = true; let isNotStr: IsString = false;
3	What are Mapped Types?	Creates a new type by iterating over the properties of an existing type	type Readonly = { readonly [P in keyof T]: T[P]; }; let ro: Readonly = { name: "Frank", age: 50 };
4	What is the keyof operator?	Gets a union of the property names of an object type	type UserKeys = keyof User; (UserKeys is "name" | "age")
5	What is the typeof operator?	Gets the type of a variable or expression	let name = "Grace"; type NameType = typeof name; (NameType is string)
6	What is the infer keyword?	Used within conditional types to infer a type from a part of a type	type GetReturnType = T extends (...args: any[]) => infer R ? R : any;
7	Explain TypeScript Module Resolution.	How TypeScript finds module files when you imports	Involves baseUrl, paths, moduleResolution compiler options in tsconfig.json
8	What is tsconfig.json?	Configuration file for the TypeScript compiler (tsc)	Specifies compiler options like target, module, outDir, rootDir, strict
9	What is the strict flag in tsconfig.json?	Enables a set of stricter type-checking options	strict: true enables noNullChecks, noImplicitAny, strictFunctionTypes, etc.
10	What are Type Declaration Files (.d.ts)?	Files that provide type definitions for JavaScript libraries that don't have TypeScript types	declare module 'lodash';, declare function jQuery(selector: string): any;
11	How do you install types for a JavaScript library?	Using @types/library-name via npm or yarn	npm install --save-dev @types/react, then import * as React from 'react';
12	What is type inference?	The process where TypeScript automatically determines the type of a variable based on its initial value	let message = "Hello"; (TypeScript infers message is string)
13	What is noNullChecks?	Requires explicit checks for null and undefined values	let name: string | null = null; if (name !== null) { ... } (prevents runtime errors)
14	What is noImplicitAny?	Prevents TypeScript from implicitly using the any type when a type cannot be inferred	let value; (causes an error if noImplicitAny is true)
15	Explain the concept of namespaces in TypeScript.	A way to organize code and provide global scope for sharing code across files	namespace Utils { export class Helper { ... } }, import helper = Utils.Helper;