TypeScript Interview Questions and Answers

Last updated on Jan 09, 2023
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TypeScript Interview Questions

The word of development is rapidly growing, so as the programming languages associated with it. TypeScript is one of these increasingly popular programming languages. We will discuss several advanced TypeScript interview questions while further continuing here for your practice. TypeScript is an object-oriented, open-source, strongly typed and compiled programming language. It’s a typed superset of JavaScript (compiled to JavaScript) and can be used for JavaScript application development supported to server-side and client-side execution.

Simplifying it, TypeScript is an advanced version of JavaScript with additional features to help both programming language and new tool requirements for developers. With the conclusion of basic TypeScript knowledge, now let’s continue with our expert-selected, crucial TypeScript interview questions with the suggested answer that may help you crack your next big interview.

Benefits of TypeScript

  • With TypeScript, the production of pure object-oriented code is possible even with limited knowledge as this is completely object-oriented programming.
  • It can be used for both server-side and client-side development alike.
  • TypeScript comes with types that make code easier to read and void major errors.
  • As it’s a package, TypeScript can be installed on projects via npm. This will make new features available and compile to all modern browsers.
  • TypeScript offers an API for DOM manipulation.
  • It also has the concept of the namespace by Module defining.
  • With IDE support here, developers will save a ton of valuable time here.

Most Frequently Asked TypeScript Interview Questions

Here in this article, we will be listing frequently asked TypeScript Interview Questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

Q11. How to enable Decorators in TypeScript via command line?

To enable decorators in TypeScript, developers first have to enable the option of experimentalDecorators via command line or tsconfig.json.

Here is the command line to use.
  • $tsc --target ES5 --experimentalDecorators
  • For tsconfig.json, use the following syntax.
       "compilerOptions": {
          "target": "ES5",
          "experimentalDecorators": true
Q12. What is static typing in TypeScript?

In TypeScript, static typing means parameters, variables, and object members have types that compiler recognizes at the time of compile. This helps in detecting early errors faster than unit test runs. It also greatly helps IDEs with auto-completion and API exploration with statically typed DOM. Static typing is an important chapter which supports a number of TypeScript Interview Questions, so it’s crucial to practice this one.

Q13. What is the prototype in TypeScript?

The prototype property in TypeScript allows users to include methods and properties to an object. It allows cloning objects (complex ones also) without coupling to their specific classes. Prototype objects can create full copies due to the accessibility of objects to each other’s private field.

Q14. What is the callback function in TypeScript?

In TypeScript, the callback function is used to schedule a call after some asynchronous processing is completed. It is passed to another function as a parameter that allows callback function to be called when the process of asynchronous processing is completed.

Q15. How to write a function in typescript?

In Typescript, a function in TypeScript can be written in two ways:

Named Function

This type of function is written and called using its own name.


function display() {
console.log("Hello Best Interview Question Team!");
display(); //Output: Hello Best Interview Question Team

Anonymous Function

In this function, the code is written and stored through expressions or variables. The variable/expression name is used to call the stored data types.


let greeting = function() {
console.log("Hello Best Interview Question Team");

greeting(); //Output: Hello Best Interview Question Team

Q16. How to declare a module in TypeScript?

Here’s how to declare modules in Typescript:

Declaring any of the external modules having no exposed types or values:

declare module 'Foo' {
   var x: any;
   export = x;

For declaring individual classes

declare module 'Foo' {
   export type cls = any;
   export var cls: any;

Q17. How to import a module in typescript?

Modules can be imported using the import keyword. Here’s a detailed info into it:

Importing individual exports from within a module:

import { Employee } from "./Employee";
let empObj = new Employee("Best Interview Question", 1);
empObj.displayEmployee(); //Output: Employee Code: 1, Employee Name: Best Interview Question

Now, to import the exports within a module as a variable into another module, use this code:

import * as Emp from "./Employee"
console.log(Emp.age); // 10
let empObj = new Emp.Employee("Best Interview Question" , 2);
empObj.displayEmployee(); //Output: Employee Code: 2, Employee Name: Best Interview Question

Q18. How to call typescript function from JavaScript?

Compiling Typescript into Javascript is done using a JS function. During this process of compiling, the code structure could be changed a bit. If you have multiple modules or classes in the typescript, then they would become a part of the path to call the specific function.


class Foo{
     public Bar = () : string =>{
         return "This is a string";
module FooModule {
     export var FooInstance = new Foo();
If you would want to call this in Typescript, use this command:
Note: The pages mentioned above have to be imported in a proper manner to call in Typescript.

Q19. How to check type of variable in typescript?

The typeof command is used to check the data type of any variable in Typescript.

Variable: abc:number|string;
if (typeof abc === "number") {
   // do something

Q20. How to use typescript in visual studio 2015?
To successfully use Typescript with Visual Studio, follow these steps:
  • Install the Typescript compiler, tsc
  • Go to the Solutions Explorer and Click on properties
  • Now, go to the Typescript Build Tab and change the Typescript version as per requirement.
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