Embarking on a TypeScript journey, whether you’re a seasoned developer or an aspiring one, often leads to a crucial milestone – the technical interview. Typescript interview questions advanced can be the gateway to unlocking exciting opportunities, but they can also seem daunting at first. Fear not, as we delve into the depths of TypeScript’s most captivating features and unravel the nuances that set the language apart.

In this article, we’ll explore the top advanced typescript interview questions and answers that will challenge your understanding and sharpen your skills. From deciphering the intricate workings of optional chaining to navigating the realm of abstract classes, we’ll equip you with the knowledge and confidence to ace your next TypeScript interview.

Top Typescript interview questions advanced

Being prepared with the best typescript interview questions advanced and answers, will help you get over the interview perfectly. Here are some of the typescript interview questions and answers:

1. How does optional chaining work in TypeScript?

this may be one of the typescript interview questions advanced, as Optional chaining, denoted by the ?. operator, allows you to safely access nested object properties without the risk of encountering a null or undefined value. This feature is particularly useful when dealing with complex data structures or API responses that may contain missing or optional properties.

An example of how optional chaining works:

typescript Copy interface User {   name: string;   address?: {     street?: string;     city?: string;   }; } const user: User = {   name: ‘John Doe’,   address: {     street: ‘123 Main St’,   }, }; console.log(user.address?.city); // Output: undefined console.log(user.address?.street); // Output: ‘123 Main St’ This one of the typescript interview questions advanced you may be asked, so answer with the example above,which shows the user.address?.city expression will return undefined instead of throwing an error if the address property is null or undefined. This ensures your code gracefully handles missing or optional data, making it more robust and error-tolerant.

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2. What are abstract classes in TypeScript?

This one of the typescript programming interview questions about abstract that you may be asked. In TypeScript, abstract classes serve as a blueprint for other classes to inherit from. They provide a way to define common properties and methods that can be shared among related classes, promoting code reuse and maintaining a consistent structure within your codebase.

Abstract classes cannot be directly instantiated; instead, they must be extended by concrete classes that implement the abstract methods defined in the parent class. This allows you to define a common interface for a group of related classes while still providing flexibility for the implementation details.

Abstract class example in TypeScript:

typescript Copy abstract class Animal {   protected name: string;   constructor(name: string) {     this.name = name;   }   abstract makeSound(): void;   move(): void {     console.log(`${this.name} is moving.`);   } } class Dog extends Animal {   makeSound(): void {     console.log(‘Woof!’);   } } const dog = new Dog(‘Buddy’); dog.makeSound(); // Output: Woof! dog.move(); // Output: Buddy is moving.

Because this probably will be one of the typescript interview questions advanced, you need to answer as we clarified with the previous example.

As this example shows, the Animal abstract class defines a name property and two methods: makeSound() (which is abstract and must be implemented by child classes) and move() (which is concrete and can be used by child classes).

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3. What are type assertions in TypeScript?

Type assertions in TypeScript allow you to explicitly specify the type of a variable or expression. This can be useful when the TypeScript compiler is unable to infer the correct type, or when you know more about the type of a variable than the compiler does.

Type assertions in TypeScript could be performed by two ways:

The as syntax:

typescript Copy let someValue: any = ‘this is a string’; let strLength: number = (someValue as string).length;

The angle-bracket syntax:

typescript Copy let someValue: any = ‘this is a string’; let strLength: number = (<string>someValue).length;

This is one of the typescript interview questions advanced, that you can answer using Both of these examples that assert that the someValue variable is of type string, allowing you to access the length property.

Type assertions are a powerful tool, but they should be used with caution, as they can bypass the TypeScript type-checking system. It’s important to ensure that your type assertions are accurate and consistently applied throughout your codebase.

4. What is the difference between type inference and contextual typing in TypeScript?

This one of the interview questions on typescript that you can answer by this:

Type Inference

This is the process by which the TypeScript compiler automatically determines the type of a variable or expression based on the context in which it is used. This allows you to write TypeScript code with less explicit type annotations, as the compiler can often infer the correct types from the surrounding code.

For example:

typescript Copy let x = 42; // TypeScript infers that x is of type number

Contextual Typing

This is a specific type of type inference that occurs when the expected type of an expression is known from the context in which it is used. This allows the TypeScript compiler to infer the type of the expression based on the surrounding code.

For example:

typescript Copy function greet(name: string) {   console.log(`Hello, ${name}!`); } greet(‘John’); // TypeScript infers that the argument is of type string

In this case, the TypeScript compiler can infer that the argument passed to the greet function should be of type string because that’s the type expected by the function’s parameter.

The key difference between type inference and contextual typing is that type inference happens throughout your codebase, while contextual typing is specific to the context in which an expression is used.

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5. How do function overloads work in TypeScript?

Function overloading is one of the important parts of the typescript, so it will surely be a part of the typescript interview questions advanced.

Function overloading in TypeScript allows you to define multiple function signatures for a single function name, each with different parameter types and return types. This can be useful when you want to provide multiple ways of invoking a function, depending on the input data.

An example of function overloading in TypeScript:

typescript Copy function add(a: number, b: number): number; function add(a: string, b: string): string; function add(a: any, b: any): any {   return a + b; } console.log(add(2, 3)); // Output: 5 console.log(add(‘Hello ‘, ‘world’)); // Output: ‘Hello world’

In this example, the add function has two overloaded signatures:

• add(a: number, b: number): number – This signature handles the case where both arguments are numbers, and the function returns a number.
• add(a: string, b: string): string – This signature handles the case where both arguments are strings, and the function returns a string.
• The third implementation of the add function, with the signature add(a: any, b: any): any, is a catch-all implementation that handles any other input types. This implementation is called if none of the overloaded signatures match the provided arguments.

Function overloading can help you create more expressive and flexible APIs, but it’s important to carefully design and manage the overloaded signatures to avoid ambiguity or unexpected behavior.

6. How to compile TypeScript with Visual Studio Code?

You should know that this may be one of the typescript interview questions advanced as Compiling TypeScript with Visual Studio Code is a straightforward process. Here are the steps:

1- Install the TypeScript compiler

Make sure you have the TypeScript compiler installed on your system. You can install it globally using npm by running npm install -g typescript.

2- Open your TypeScript file in VS Code

Create a new TypeScript file (e.g., example.ts) or open an existing one.

3- Configure the TypeScript compiler settings (optional)

By default, VS Code will use the global TypeScript compiler settings. If you need to customize the compiler options, you can create a tsconfig.json file in your project directory and configure the settings there.

4- Compile the TypeScript file

There are a few ways to compile your TypeScript file in VS Code: 

• Automatic compilation: VS Code can automatically compile your TypeScript file as you’re writing it. To enable this, go to the VS Code settings (File > Preferences > Settings) and search for “TypeScript: Auto Compile” and enable it. B
• Compile on save: VS Code can also compile your TypeScript file every time you save it. To enable this, go to the VS Code settings and search for “TypeScript: Watch Option” and set it to “afterSave”. 
• Manually compile: You can also manually compile your TypeScript file by pressing Ctrl+Shift+B (Windows/Linux) or Cmd+Shift+B (macOS) to bring up the VS Code build task menu, and then select the “TypeScript – Compile” option.

Once you’ve compiled your TypeScript file, VS Code will generate a corresponding JavaScript file (e.g., example.js) in the same directory, which you can then use in your application.

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7. What are the Recent Advancements in TypeScript?

This will probably be one of the typescript interview questions advanced, because TypeScript has continuously evolved since its introduction, with the language team at Microsoft regularly releasing new versions with various improvements and features. Here are some of the recent advancements in TypeScript:

Awaited Type

The Awaited utility type was introduced in TypeScript 4.5, simplifying the process of working with Promise-based asynchronous code. It helps to infer the resolved type of a Promise, making it easier to handle the results of asynchronous operations.

Promise Improvements:

TypeScript 4.5 also brought improvements to Promise-related types, including the ability to use Promise<T> in type annotations and the introduction of the PromiseType utility type.

Node.js Module Support:

Starting from TypeScript 4.7, the language now supports ES6 modules (import/export) in Node.js environments, making it easier to integrate TypeScript with modern JavaScript ecosystems.

Recursive Type Aliases:

TypeScript 4.1 introduced recursive type aliases, which allow you to create complex, self-referential type structures, such as linked lists and trees.

Improved Tuple Types:

TypeScript 4.0 enhanced tuple types, making them more flexible and expressive. This includes support for variadic tuple types and better type inference for tuple assignments.

Template Literal Types:

TypeScript 4.1 introduced template literal types, which enable you to create types based on string literals, enabling more advanced type-level programming techniques.

Improved Inference for Function Parameters:

TypeScript 4.0 improved type inference for function parameters, making it easier to write concise and expressive code without the need for explicit type annotations.

These are just a few highlights of the recent advancements in TypeScript. The language continues to evolve, adding new features and improvements to enhance developer productivity and code maintainability.

8. Explain the Awaited Type and Promise Improvements in TypeScript

This may be one of the typescript interview questions advanced you may be asked, you can answer stating that:

The Awaited type in TypeScript is a utility type that simplifies working with Promise-based asynchronous code. It helps to infer the resolved type of a Promise, making it easier to handle the results of asynchronous operations.

An example of how the Awaited type can be used:

typescript Copy // Without Awaited type async function fetchUser() {   const response = await fetch(‘/api/user’);   const user = await response.json();   return user; } type User = ReturnType<typeof fetchUser>; // With Awaited type async function fetchUser() {   const response = await fetch(‘/api/user’);   const user = await response.json();   return user; } type User = Awaited<ReturnType<typeof fetchUser>>;

In the second example, the Awaited type is used to infer the resolved type of the fetchUser function, which returns a Promise. This eliminates the need for the explicit ReturnType type utility, making the code more concise and easier to read.

In addition to the Awaited type, TypeScript 4.5 also brought improvements to Promise-related types, including:

• Ability to use Promise<T> in type annotations: You can now use Promise<T> in type annotations, which makes it easier to work with Promise-based APIs.
• Introduction of the PromiseType utility type: The PromiseType utility type allows you to extract the resolved type of a Promise, similar to the Awaited type but without the need for an await expression.

These improvements to Promise handling in TypeScript help to make asynchronous code more manageable and less error-prone, particularly in larger-scale applications that rely heavily on asynchronous operations.

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9. How TypeScript files can be supported from Node Modules?

This may be one of the typescript interview questions advanced you may be asked, you can answer stating that:

Starting from TypeScript 4.7, the language now supports ES6 modules (import/export) in Node.js environments, making it easier to integrate TypeScript with modern JavaScript ecosystems.

Before TypeScript 4.7, developers often had to use the require() function and the CommonJS module system to import and use TypeScript files in a Node.js environment. This required additional configuration and setup, which could be cumbersome.

With the introduction of ES6 module support, you can now use the standard import and export syntax to work with TypeScript files in a Node.js project. Here’s an example:

typescript Copy // file1.ts export const message = ‘Hello, TypeScript!’; // file2.ts import { message } from ‘./file1’; console.log(message); // Output: ‘Hello, TypeScript!’

To enable this functionality, you need to configure your tsconfig.json file to use the “module”: “ES6” (or “module”: “ESNext”) setting. This tells the TypeScript compiler to output ES6 modules instead of CommonJS modules.

Additionally, you’ll need to ensure that your Node.js environment supports ES6 modules. This can be done by setting the “type”: “module” field in your package.json file, or by using the .mjs file extension for your TypeScript files.

Once you’ve made these configurations, you can seamlessly import and export TypeScript modules within your Node.js application, just like you would with regular JavaScript files. This integration between TypeScript and modern module systems simplifies the development and deployment of TypeScript-based applications in a Node.js environment.

10. What is Recursive Type Aliases?

This will probably be one of the typescript interview questions advanced, because Recursive type aliases in TypeScript allow you to create complex, self-referential type structures, such as linked lists and trees. This feature was introduced in TypeScript 4.1 and provides a powerful way to model and work with data structures that contain elements of the same type.

An example of a recursive type alias for a singly-linked list:

typescript Copy type LinkedList<T> = {   value: T;   next?: LinkedList<T>; }; // Create a linked list const list: LinkedList<number> = {   value: 1,   next: {     value: 2,     next: {       value: 3,       next: undefined,     },   }, };

In this example, the LinkedList type alias is recursive, as the next property is of the same type (LinkedList<T>). This allows you to create complex, nested data structures that can be easily represented and manipulated in TypeScript.

Recursive type aliases can be particularly useful when working with data structures that have a hierarchical or tree-like structure, such as file systems, organization charts, or DOM trees. By using recursive types, you can create type-safe representations of these structures and leverage TypeScript’s type-checking capabilities to ensure the correctness of your code.

It’s important to note that when using recursive type aliases, you should be mindful of the potential for infinite recursion, which can lead to performance issues or even crashes. Proper error handling and input validation are crucial when working with recursive data structures.

Overall, recursive type aliases are a powerful feature in TypeScript that enable you to model and work with complex, self-referential data structures in a type-safe and expressive way.
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