Interviewing Typescript

In this tutorial, we will delve into the world of TypeScript and explore some important interview questions and their corresponding answers. TypeScript, a statically typed superset of JavaScript, brings enhanced features and static type-checking to JavaScript development. By understanding these questions and answers, developers can gain insights into TypeScript's core concepts and capabilities.

TypeScript Basics

Here are some important questions that cover the basics of TypeScript −

What is TypeScript, and how Does it Differ From JavaScript?

TypeScript is a programming language that extends JavaScript by introducing optional static typing and additional features. While JavaScript is a dynamically typed language, TypeScript allows developers to explicitly declare types for variables, function parameters, and return values. This brings the benefit of early error detection during development, as the TypeScript compiler checks for type inconsistencies and provides helpful feedback.

What are the key Features of TypeScript?

The key features of TypeScript are −

• Static Typing − TypeScript allows developers to declare and enforce types, catching errors early.

• Enhanced Tooling − TypeScript offers advanced development tools for improved productivity.

• ECMAScript Compatibility − TypeScript is compatible with existing JavaScript codebases.

• Code Maintainability − TypeScript promotes better code organization, understanding, and scalability.

• Object-Oriented Programming Support − TypeScript supports classes, interfaces, inheritance, and access modifiers.

• Module System − TypeScript has a built-in module system for managing code dependencies and reusability.

How Does TypeScript Help Catch Errors During Development?

TypeScript helps catch errors during development by performing static type checking. It analyses the code and its declared types without executing it. This process allows TypeScript to identify type-related errors and inconsistencies early in the development process. By catching these errors before running the code, developers can address them proactively, reducing the chances of encountering bugs or unexpected behavior during runtime.

TypeScript Types and Type System

Here are some important questions that cover typescript types and type system

What are the Basic Types in TypeScript?

In TypeScript, the basic types include boolean, number, string, array, tuple, enum, any, void, null, and undefined. These types cover common data representations such as logical values, numbers, text, arrays of elements, fixed-sized arrays with different types, named constant values, dynamic values, absence of values, and uninitialized variables.

What is the Purpose of Type Annotations in TypeScript?

The purpose of type annotations in TypeScript is to explicitly declare the types of variables, function parameters, and return values. By providing type annotations, developers can define the expected data types and enforce type safety in their code. Type annotations help catch errors and inconsistencies early during development, as the TypeScript compiler analyzes the code and verifies that values are used correctly according to their declared types.

How Does TypeScript Handle Type Checking?

TypeScript performs type checking through a process known as static type checking. During compilation, the TypeScript compiler analyzes the code and verifies that the types of variables, function parameters, and return values align with their respective type annotations and expected usage.

What is the difference between null and undefined in TypeScript?

In TypeScript, null and undefined are both used to represent the absence of a value, but they have slight differences −

• null is a value that can be assigned to a variable intentionally to indicate the absence of an object value. It is a specific value of the null type.

• undefined typically represents the absence of a value or an uninitialized variable. It is a type in TypeScript that is automatically assigned to variables that have not been assigned a value.

While both null and undefined are considered falsy values, they are distinct types in TypeScript. Variables of type null can only be assigned the value null, while variables of type undefined can only have the value undefined.

Object-Oriented Programming in TypeScript

Here are some important questions that cover Object-Oriented programming in TypeScript

How does TypeScript Support Object-oriented Programming (OOP)?

TypeScript supports object-oriented programming (OOP) principles and features, allowing developers to write code in an object-oriented style. Here are some ways TypeScript supports OOP −

• Classes − TypeScript allows the creation of classes using the class keyword. Classes encapsulate data and behavior into objects, providing a blueprint for creating instances. They support features like inheritance, constructors, properties, and methods.

• Inheritance − TypeScript supports class inheritance, allowing classes to inherit properties and methods from parent classes. This promotes code reuse and hierarchy in class relationships.

• Encapsulation − TypeScript supports encapsulation through access modifiers (public, private, and protected). These modifiers control the visibility and accessibility of class members, ensuring proper encapsulation and information hiding.

• Polymorphism − TypeScript supports polymorphism, allowing objects of different classes to be treated as instances of a common parent class or interface. This enables code flexibility and the ability to define generic behavior across multiple classes.

• Interfaces − TypeScript provides interfaces that define contracts for objects. Interfaces describe the structure and behavior that classes must adhere to. They promote loose coupling, abstraction, and contract-based programming.

• Abstract Classes − TypeScript supports abstract classes, which are classes that cannot be instantiated but can serve as base classes for other classes. Abstract classes define common properties and methods that subclasses must implement.

By offering these features, TypeScript facilitates the creation of modular, reusable, and structured code using object-oriented programming principles.

What are Access Modifiers (Public, Private, Protected) in TypeScript?

Access modifiers in TypeScript are keywords used to control the visibility and accessibility of class members (properties and methods). Here's a brief explanation of each access modifier −

• public − Public members are accessible from anywhere, both within the class and externally. They can be accessed and modified by any part of the code.

• private − Private members are only accessible within the class that defines them. They cannot be accessed or modified from outside the class, including subclasses.

• protected − Protected members are accessible within the class that defines them and their subclasses. They cannot be accessed from outside the class hierarchy.

Advanced TypeScript Concepts

Here are some important questions that cover advanced TypeScript concepts −

What are Generics, and how are They Used in TypeScript?

Generics in TypeScript allow for the creation of reusable code components that can work with different types. They provide a way to define type parameters that can be specified when using the component. Generics are indicated using angle brackets (<>) and can be used to parameterize functions, classes, and interfaces to work with different types dynamically.

What is the Purpose of the Readonly Modifier in TypeScript?

The readonly modifier in TypeScript is used to indicate that a property or variable should be read-only, meaning its value cannot be modified once it is assigned. It provides a way to enforce immutability and prevent accidental modifications to specific data.

Through this comprehensive interview question and answer tutorial, users have explored a wide range of important topics related to TypeScript. By understanding these concepts, users are better equipped to utilize TypeScript's features effectively and build robust, scalable applications. Remember to continue exploring TypeScript's documentation and practice implementing these concepts in real-world scenarios to enhance TypeScript skills and expertise further.