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TypeScript Interview Questions and Answers

TypeScript Interview Questions and Answers

May 17th, 2019

TypeScript Interview Questions and Answers

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Best TypeScript Interview Questions and Answers

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Typescript Questions & Answers

Q1) A web application developer is working on a requirement where in he has to develop the application in such a way that it should be scalable. Which among the below TypeScript feature makes him to select TypeScript for his application?

Answer: Modules

Q2) TypeScript can be installed by which among the following?

Answer: Downloaded as node module from the NPM repository

Q3) Which among the below statements are true regarding TypeScript?

Answer: TypeScript is extended from ECMAScript, TypeScript has to be converted to JavaScript to use it in a Webpage

Q4) A web application developer is working on a requirement using JavaScript. Which of the below TypeScript feature made him to select TypeScript for his application?

Answer: Statically typed Scalability

 Q5) Predict the output of below code snippet?

var var1=100;
        var var1=200;
let var2=200;
            let var2=100;

Answer: 200 200 100 200

Q6) Predict the output of the below code: enum Size{Small=32,Medium,Large=40};

Answer: The medium size is 33

Q7) Predict the output of the below code:

 function sayHi(person: string) {   return “Hello, ” + person; }

var customer :string[] = [“Tom”, “Harry”, “Jack”]; document.body.innerHTML = sayHi(customer);

Answer: Compilation Error

 Q8) Predict the output of the below code:

let color: string[] = [“red”,”green”,”blue”];console.log(color.pop());

Answer: Blue

Q9) Consider the code snippet given below: let productId: [string, number]; productId= [“Mob342″, 675, 7845,”Tab673”];

Answer: This code will throw compilation error, due to length restriction. This code will get executed if two values are passed of declared data type

Q10) What will be the output of the below code snippet?

function add(n1:number,n2:number):number{
             let total:number=n1+n2;             return true;

 Answer: Compilation Error

Q11) Predict the output of the below code?

function  add(num1:number,num2?:number) {
        return num1+num2;
    }    return num1;

Answer: 16

Q12) What will be the output of the below code snippet? Select the correct statement/s from the below regarding TypeScript Interface:

i]  Protected members can be declared

ii] Only private members can be declared

iii] The members declared are public by default

Answer: Only iii] is true

 Q13) Predict the output of below code snippet.

interface calcy {
class display implements calcy {
    x: number;
         mul(n:number) {
            this.x =n * n;         
        mul(n:string) {
            this.x =n + n;         
let arr = new display;
arr.x = 0;     

Answer: Compilation Error

Q14) What does it mean by Semantic HTML?

Answer: Semantic HTML is a type of coding style in which tags will have texts that need to display on the user interface.
Bold, Italic tags should not be used to represent Semantic HTML

Q15) How does a responsive website differ from the normal website?

Answer: Responsive website fits for every screen resolution that looks good. In case of normal websites, it would fit only for selected screen resolutions.

Q16) What is meant by inline?

Answer: Elements follow the same flow without breaking. This will push other elements horizontally if margin/padding is added. Ignores height and width.

Q17) What is meant by block?

Answer: Elements with block will break the line. Example: div, padding

Q18) What is meant by inline-block?

Answer: It looks the same as inline elements. The difference is that it considers height and width.

Q19) What is mean by document and window? How it differs?

Answer: Js has a global object in which everything runs in it which is called a window.
Document works under window object. It represents DOM.

Q20) How javascript hoisting works?

Answer: In JS, variables/functions have to defined earlier at the top before using it. It throws error if it is not accessible.

Q21) What is mean by event bubbling?

Answer: Bubbling is when an event is triggered on the element it carries the event entirely up through the DOM tree.

Q22) What is mean by event capturing?

Answer: Bubbling is when an event is triggered on the element it carries the event entirely down through the DOM tree.

Q23) What are the best ways to reduce page load time?

Answer: Image memory size, unwanted scripts, compression, external files should be reduced to have a better page load time.

Q24) How HTML works with a compiler?

Answer: No, HTML doesn’t need compiler since it is a front end language.

Q25) How web accessibility works?

Answer: Web accessibility means to provide access to the website for differently-abled and disabled persons they can understand easily.

Q26) What is meant by local storage?

Answer: Local storage allows the user to store data without any expiry limits. It is reachable at any time.

Q27) How floating works?

Answer: It pushes the element left or right based on the element tags.

Q28) How to optimize website performance?

Answer: CDN hosting, compression, concatenation, refining code and reorganizing.

Q29) What kind of things must you be aware of design or developing for multilingual sites?

Answer: Default language setting using Unicode encoding, using the “lang” attribute.
Aware of fonts and directions of the language.

Q30) What would be the difference between HTML, elements and tags?

Answer: HTML elements communicate to the browser which will render text. When angular brackets <> are added they form HTML tags.

Q31) How does Doctype works?

Answer: The term DOCTYPE informs the browser which type of HTML is used on a webpage. The browsers use DOCTYPE to check how to render a page.

Q32) what is standard and quirks mode? How it differs?

Answer: Quirks Mode is a default compatibility mode that will be different from browser to browser and it may result in a lack of consistency in appearance from browser to browser.

Q33) What are the limitations/limits when using XHTML pages?

Answer: Poor browser supports XHTML. Internet Explorer and other agents cannot parse XHTML as XML.
What is meant by the CSS Box Model?
CSS Box Model includes content, margin, padding, and border. Total border-box width is equal to width + padding + border. These properties occupy space on the CSS box model.

Q34) What is the difference between display none and visibility hidden?

Answer: Visibility: hidden hide the content from the user but retain space. Whereas Display: none hide the content and remove space.

Q35) What is difference between == and === operator?

Answer: == is comparison operator, whereas === is hard equality. == checks value only, === check value and datatype. 5==”5″ is true, but 5===”5″ is false.

Q36) What is the use of jquery ready function?

Answer: Jquery recommends use of $(document).ready(function(){ }) or $(function(){ }) in script tag to write jquery syntax. Jquery ready function execute Jquery functions after all html elements are loaded, before images, iframes, ads are loaded.

Q37) What are the overcomes of CSS?

Answer: Ascending by selectors is not possible
Limitations of vertical control
No expressions
No column declaration
Pseudo-class not controlled by dynamic behavior
Rules, styles, targeting specific text not possible

Q38) What are the advantages of ruleset?

Answer: The ruleset is used to identify that selectors can be attached to other selectors. It has two parts:
Selector – Selector indicates the HTML element you want to style.
Declaration Block – The declaration block can contain one or more declarations separated by a semicolon.

Q39) What are the uses of External Style Sheets?

Answer: You can create classes for reusing it in many documents.
By using it, you can control the styles of multiple documents from one file.
In complex situations, you can use selectors and grouping methods to apply styles.

Q40) What are the advantages of CSS sprites?

Answer: If a web page has a large number of images that take a longer time to load because each image separately sends out an HTTP request. The concept of CSS sprites is used to reduce the loading time for a web page because it combines the various small images into one image. It reduces the number of HTTP requests and hence the loading time.

Q41) What is called tweening and why?

Answer: It is the process of generating intermediate frames between two images.
It gives the impression that the first image has smoothly evolved into the second one.

Q42) It is an important method used in all types of animations.

Answer: In CSS3, Transforms (matrix, translate, rotate, scale) module can be used to achieve tweening.

Q43) How CSS property default value can be restored?

Answer: In short, there is no easy way to restore to default values to whatever a browser uses.
The closest option is to use the ‘initial’ property value, which restores the default CSS values, rather than the browser’s default styles.

Q44) What is the use of TypeScript and why we should use this?

Answer: TypeScript compiles to JavaScript and used to call superset as well of JavaScript. It’s contains additional features of JavaScript like OOPS,Assignment,data types.It helps to make the code more dynamic based on data types.

Q45) What are the key Benefits of TypeScript ?

Answer: Below are the key features of TypeScript : –

  • It’s fast and easy to learn as simple syntax. It’s run on any browser.
  • It helps to write front-end code fast.
  • It’s superset of JavaScript so support all the features and provided additional features.
  • it’s provide features from ES5/ES6/ES7 and can be used in front-end and Node Js.

Q46) List out all the components of TypeScript?

Answer: Below are the components of TypeScript :-

  • Language
  • TSC-(TypeScript Compiler)
  • TSLS- (TypeScript Language Service)

Q47) What are the various types of TypeScript ?

Answer: It has two types

  • Built-in – This contains boolean , String, Number,null, void and undefined.
  • User-defined -It contains Interfaces,Classes,arrays,tuple,enumeration

Q48) What are the OOPS(Object Oriented) terminology support by TypeScript?


  • Interfaces
  • Classes
  • Modules
  • Data Types
  • Inheritance
  • Member functions

Q49) Function overloading can be achieve in TypeScript ?

Answer: Yes, TypeScript supports function overloading. TypeScript only have one implementation. Below is the example for the same.

Class Employe {
empName: string;
empId: number;
createEmployee(empId: number);
createEmployee(value: any) {

Q50) What is scope variable in TypeScript?

Answer: In TypeScript Objects,Function,variables,objects can have local and global scope variable. Below described both the types.

Local Scope – It is used within the function so scope will be limited to that function object.

Global Scope –This can be used within and outside the funtion as used to declare as Global.

Q50) How to call Parent class constructor from Child class in TypeScript?

Answer: super() function used to call parent class constructor from child class constructor.

Q51) Default visibility for class attributes in TypeScript ?

Answer: Default visibility is Public for all attributes.

Q52) Describe Interface in TypeScript ?

Answer: Interface used to defined and achieve pure abstraction. Interface contains variable/method declaration.

Q53) What is the role of Omit type in TypeScript?

Answer: It’s used to exclude the properties from original type.

Q54) How all properties can make of an Interface optional in TypeScript?

Answer: Partial mapped type can be used to make all properties.

Q55) Where decorators can be used in TypeScript ?

Answer: Methods,Classes, Method Arguments, Properties.

Q56) What is the use of Record Type in TypeScript ?

Answer: This used to create Typed Map.

Q57) What is the use of Unknown keyword and when to use it ?

Answer: If you are not aware with the exact data type and do not want to use “any” then “Unknown” can be used to define.

let employee: unknown = ‘Kabir Singh’;

Q58) Why we should use Arrow Function in TypeScript ?


  • It’s doesn’t contain unnecessary code and give shorter way to define the functionality.
  • Arrow function binds “this” automatically to the code’s context.
  • Shorter and more simple to define.

Q59) What is the command to install TypeScript ?

Answer: npm install -g typescript

Q60) How to define an array in TypeScript ?


var empName:string[]; //Declaration Part

empName=[“Swami”,”Pandey”,”Rajni”,”Rakesh”] //Initialization

Q61) What is the use of Constructor in TypeScript ?

Answer: Constructor used to do member’s Initialization of the class.

Q62) How String can be convert to Number in TypeScript ?

Answer: Below is the snippet code to convert String to Number

this.empId = Number(empName);

Q63) Anonymous function in TypeScript?

Answer: This function doesn’t have name identified. Below is the snippet code for the same.

let annonyFun = function(p: number, q: number) {

return p – q;



Q64) What are the file Naming Extension’s in TypeScript?

Answer: There are two extension’s – .tsx  , .ts

Q65) What is tuple in TypeScript?

Answer: Tuple is collection of heterogeneous values or it store multiple different-different type data type values. Below is the example for the same.

var fileData = [“Alia”,90,”Shweta”,45];

Q66) What is Union in TypeScript?

Answer: When need to combined two or more data type then pipe “|” symbol to denote a Union Type. Below is the example for the same.

var userId:string|number



Q67) What is the use of split() method in TypeScript ?

Answer: This method split string to an array with a separator. Below is definition for the same.

var quote=”Life is all about the next step”;

var splittedQuote=quote.split(” “,5) // Here 5 is the limit and space is separator


Q68) What is Implicit module in TypeScript ?

Answer: When you don’t need to import anything to write your source code this is call as implicit module.

Q69) Can we combine multiple .ts file in to single .ts file in TypeScript ?

Answer: Yes, In TypeScript we can do this.

Q70) What is new keyword in TypeScript ?

Answer: This keyword required to initialize object.

Q71) List out the access modifiers in TypeScript ?


  • Protected
  • Private
  • Public

Q72) Describe pop() and push() method in tuple ?


pop() – this used to append the value

pop()- this used to removed and return the last value