TypeScript Interview Questions and Answers

TypeScript is an object-oriented, open source programming language maintained and developed by Microsoft. It is developed to overcome the flaws of JavaScript. As a superset of JavaScript, TypeScript can be used to develop large JavaScript applications with support for modules and classes, ES6 features, Type-checking, API definition, JavaScript packaging support, class library, and more.

Steps to install TypeScript environment in Windows are given below.

• First, download the latest version of TypeScript from its official website.
• We can install TypeScript using Node.js, Visual Studio, or other supported editors, but the first two are the most common way to install it.
• Download and run the .msi installer for Node support.
• Then, we will use npm to install TypeScript using Node.js. Just running the below-mentioned command in the Windows command will install the latest version.
  npm install -g typescript
• We can check the version of TypeScript by running the following command in the terminal.
  tsc -v
• To get help for other options here, use the following command
  tsc -h
• To install TypeScript using Visual Studio, download Visual Studio Code, and launch it.
• Now by right clicking on the file → open in the command prompt, users may traverse to the file’s path.
• Now, creating a TypeScript file is possible just by adding a new file with a .ts extension. All the features of TypeScript will be available out of the box

The Typescript components comprise 3 parts. They are:

• Language: It consists of features of the language element of Typescript. Syntax, keywords, and type annotation rules and syntax are covered in this.
• The TypeScript Compiler: Used to compile the same code into Javascript. It also parses and checks the type of code being compiled into Javascript.
• TypeScript Language Services: This provides information that helps editors and other tools to increase productivity by automated refactoring and Intellisense.

TypeScript developers can use the access modifiers to control the accessibility of the class members. There are two types of access modifiers in TypeScript; private and public modifiers. Class members are public by default, but users can add a private modifier if they wish.

Super is a TypeScript keyword which can be used by developers in expressions for base class constructor and base class properties reference. This call is only allowed in constructors of derived classes. Call for this keyword consist the keyword super with an argument list closed in parentheses.

In TypeScript, an extra line is added to the JS code using the export class which is then used to add an exported item within a module.

Developers add tsconfig.json file or TypeScript configuration file to a project to guide the compiler as the JavaScript files are generated by it. This file also contains flags and options that are essential to run Angular applications.

This one is a regular TypeScript interview question that almost every candidate faces. Here are the basic data types present in TypeScript described below.

• Number Types: In TypeScript, number values are floating values which have a type of number. Users can assign any numeric value, including hexadecimal, binary, decimals, and octal literals also.
• String Types: When a user desires to implement textual data, string types will be needed. It gets denoted by the keyword string.
• Boolean Types: It is used for declaring variables and accompanied by the keyword boolean.
• Enum Type: It can be used for numeric values with friendly names. It is declared with the keyword of “enum.”
• Void Types: Used for the function that doesn’t return any value.
• Null Types: Used to declare a variable type null. It can be assigned to boolean and number value.
• Undefined Types: It is used to store the value undefined.
• Any Types: It can be implemented to ensure data value to declare said values.
• Never Types: It represents the data type of values that never occur.
• Array Type: Used to declare data arrays.
• Tuple Types: This data type allows users to create an array where the fixed number type elements are known but not the same.

Mixins are used in the creation of small and reusable objects in Typescript. You can now compose the selected objects into larger objects through multiple inheritances. Then, use it to share the common components between classes while reusing the components from one single class to parallelly run two classes in Typescript.

Yes, it's possible. To successfully merge multiple TS files together in a JS file, use a module bundler system or a Gulp Script to concatenate everything into a single JS file.