TypeScript is an open-source language developed by Microsoft. It acts as a superscript of JavaScript. It is mainly used when developing large applications. It can also be used when building JavaScript applications on both the client and server sides. It can be described as both a language and a set of tools. It supports various JS libraries and is portable. Let us look at some questions you might be asked if you attend an interview on TypeScript.
If you are looking for a job related to TypeScript, you need to prepare for the 2026 TypeScript interview questions. Every interview is different for different job profiles, but to clear the interview, you still need to have good, clear typescript knowledge. Here, we have prepared important TypeScript interview questions and answers to help you succeed in your interview.
Below are 10 important TypeScript interview questions and Answers that are frequently asked in interviews. These questions are divided into parts as follows:
Typescript Interview Questions (Basic)
This first part covers basic Interview Questions and Answers.
Q1) Explain what Typescript is, and how it is different from JavaScript?
Answer:
TypeScript is a superset of JavaScript and is used to develop large applications. It provides optional static typing, classes, and interfaces. It can be described as both a language and a set of tools. It helps developers use highly productive tools and refactor code. The main differences between Typescript and JavaScript are:
TypeScript supports classes, enabling programmers to work more in an object-oriented way, while JavaScript uses functions and prototype-based inheritance. JavaScript does not have interfaces; TypeScript does. Static typing is supported in TypeScript, but not in JavaScript. Typescript provides optional parameters; JavaScript does not.
Q2) Which are the different data types that are supported by TypeScript, and explain how to implement inheritance?
Answer:
TypeScript also supports the data types used in all other languages. It includes:
- Boolean: This can have values as true or false
- Number: This can be any number value
- String: This can be any character value
- Array: This can be a list of numbers together
- Enum: This allows you to create a user-defined data type.
Inheritance can be implemented in Typescript by using the extends keyword.
class Car {
public domestic:boolean;
constructor(public name: string) { }
}
class SUV extends Car {
constructor(name: string, domestic: boolean)
{
super(name);
this.domestic = true;
}
}
class Sedan extends Car {
constructor(name: string, domestic: boolean)
{
super(name);
this.domestic = false;
}
}
Let us move on to the next TypeScript interview questions.
Q3) Explain the tsconfig.json file?
Answer:
This file indicates that the directory is the root of the TypeScript project. This file specifies that root files and compiler options are required to compile that particular project. This file can also be used to streamline project development. The sample below can be taken as an example:
{
"compilerOptions": {
"removeComments": true,
"sourceMap": true
},
"files": [
"main.ts",
"othermodule.ts"
]
}
Q4) Explain Lambda/Arrow functions in Typescript?
Answer:
The arrow function is an additional feature in TypeScript and is also known as a lambda function. This function is without a name.
var mulNum = (n1: number, n2: number) => n1 * n2;
In this example, => is the lambda operator, (n1 * n2) is the function body, and n1 and n2 are the parameters.
let addNum = (n1: number, n2: number): number => { return n1 + n2; }
let multiNum = (n1: number, n2: number): number => { return n1 * n2; }
let dividNum = (n1: number, n2: number): number => { return n1 / n2; }
addNum(10, 2);// Result - 12
multiNum(10, 2);// Result - 20
multiNum(10, 2);// Result – 5
Q5) What is the Anonymous function?
Answer:
This function is declared without any named identifier to refer to it.
var anonyFunc = function (num1: number, num2: number): number {
return num1 + num2;
}
//RESULT
console.log(anonyFunc(10, 20)); //Return is 30
//RESULT
console.log(anonyFunc(10, "xyz"));
// error: This will throw an error as string is passed instead of an integer.
Typescript Interview Questions (Advanced)
Let us now look at advanced TypeScript interview questions.
Q6) How can a class defined in a module be used outside the module?
Answer:
Classes defined in a module are available within the module and cannot be accessed from outside it.
module Vehicle {
class Car {
constructor (
public make: string,
public model: string) { }
}
var audiCar = new Car("Audi", "Q7");
}
var fordCar = Vehicle.Car("Ford", "Figo");
The variable fordCar will give an error as the class Car is not accessible and the user needs to use export keyword for the classes.
module Vehicle {
export class Car {
constructor (
public make: string,
public model: string) { }
}
var audiCar = new Car("Audi", "Q7");
}
var fordCar = Vehicle.Car("Ford", "Figo");
This variable will now work as an export to make the Car accessible outside its module.
Q7) What are decorators, and list some of the decorators in TypeScript?
Answer:
Decorators enable a user to modify a class and its members. It allows the user to add annotations and Metaprogramming syntax to define class declarations and members. These were just released on an experimental basis. Decorators can be enabled using a command line or by editing the tsconfig.json file. To enable decorators using the command line, the following command should be used:
tsc --target ES5 --experimentalDecorators
Q8) How to compile a TypeScript file?
Answer:
The following steps should be followed in order to compile a TypeScript file:
- A user must check whether the TypeScript engine is enabled. A user can go to the title bar, check for their username and select options.
- In the project navigator, select and right-click the TS files that are to be compiled.
- Select compile to JavaScript
- A user can add a script reference to this compiled JavaScript file in HTML code.
- Once this is done, the user can go to the command line and type tsc <TypeScript File Name> to compile.
Let us move on to the next TypeScript interview questions.
Q9) What are the Interfaces in TypeScript?
Answer:
The interface defines the syntax of any variable or entity. Interfaces define properties, methods, and various events. Here, only members are declared. Interfaces help define various members and provide a structure for the derived classes. Interfaces can be declared using the interface keyword.
Q10) Why is TypeScript called an optionally statically typed language?
Answer:
TypeScript, being an optionally statically typed language, allows the compiler to ignore a variable’s type. Using any data type, the user can assign a value to any variable. Typescript will not throw any error.
var unknownType: any = 4;
unknownType = "Okay, I am a string";
unknownType = false; // A boolean.
Using this, any data type can be declared.
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