typescript interview questions and answers

Top 20 TypeScript Interview Questions and Answers

1. define typescript

Answer: A compiler can accept TypeScript as a superset of JavaScript and create ordinary JavaScript from it because it is explicitly typed.

Dealing with JavaScript in a completely object-oriented context is made possible by TypeScript. Use classes and interfaces in this situation. It is also labeled like C# or Java. You will need a TypeScript compiler to convert the code into a JavaScript file, which you can then use.

The TypeScript compiler converts a TypeScript file with the a.ts extension into a JavaScript file. Here, with various editors including VS Code, Sublime, etc., you can produce TypeScript.

2. What are the benefits of TypeScript?

Answer: Benefits include:

  1. TypeScript is simple, fast, and easy to understand, and it can run JavaScript everywhere. As a result, it ranks as one of the top frameworks for newcomers to front-end programming.
  2. JavaScript developers can switch to TypeScript because it is sufficiently comparable to JavaScript.
  3. The ability to write TypeScript using an IDE accelerates development and can result in more protected, flexible products.
  4. TypeScript code can be called from JavaScript code, providing compatibility for older JavaScript-based programs.
  5. It includes ES6 and ES7 capabilities that can be used with JavaScript ES5 engines such as Node.js.
  6. It complies with ECMAScript requirements. Your TypeScript code can be compiled for whatever ECMAScript targets you choose. This enables you to take advantage of the features and other features of ES2015. Modules, lambda functions, restructuring, etc. are some examples of these capabilities.
  7. It gives JavaScript-type support.
  8. Since an IDE can be used, TypeScript programming is a much better experience for general JavaScript development.
  9. If severe null checking is enabled using TypeScript, the TypeScript compiler will only allow you to write unknowns to a variable if you have specifically specified it as a nullable type.
  10. TypeScript is supported by Microsoft and is available under the Apache 2 license.
  11. Because TypeScript and JavaScript are interoperable, TypeScript can be used immediately by developers who are already familiar with JavaScript.

3. What are the drawbacks of TypeScript?

Answer: There are some disadvantages here.

  1. Because TypeScript code must be compiled, the implementation of TypeScript components can be slower than in JavaScript.
  2. Abstract classes are not supported by TypeScript.
  3. A TypeScript application will require an additional compilation step when running in a browser, which can have a negative impact on speed.
  4. Working with third party libraries couldn’t be easier.

4. What are the constituent elements of TypeScript?

Answer: TypeScript has three levels. The language normally consists of the following when installed:

  1. The language is often run using an IDE.
  2. A compiler that turned TypeScript directly into JavaScript code.
  3. Language service, which provides editor functions on already existing TypeScript code.

5. What do TypeScript types do?

Answer: We’ll start asking more technical questions now. The types of values ​​we use in our programs are known as types in TypeScript. It supports a wide range of value types, including integer, text, and boolean values, in addition to other types such as enum, none, and never.

Types should always be explicitly declared in TypeScript for several reasons. Types make code more readable and clear, and they can also help your compiler identify issues that result from improper type assignment. Additionally, types provide an additional layer of documentation that can be useful when working in a team context.

6. What types of data are primitives?

Answer: These are the options:

  1. number
  2. string
  3. boolean
  4. bigint
  5. sign, symbol
  6. undefined
  7. Zero

7. What are the special data types of TypeScript?

Answer:

  1. any
  2. Zero
  3. never

8. What scope does TypeScript offer?

Answer: As far as variables are concerned, there are three areas:

  1. local
  2. Celebration
  3. Global

Var is used to create both functions and global variables, whereas const and let can be applied to both.

9. In TypeScript, what are interfaces?

Answer: What unique entity, a TypeScript interface, enables us to create objects with specific properties? Let’s go ahead and build one. For example, to install the TypeScript interface, we can start by entering the reserved word interface.

10. What are the Different TypeScript Features?

Answer: The following features:

  1. It only contains JavaScript.
  2. It supports more JS libraries.
  3. It is transportable.

11. Does method/function overloading work with TypeScript?

Answer: The answer is that function overloading is available in TypeScript. Many functions may have the same name and number of arguments, but the return type and parameter type need to be different. Overloading of functions with the same name, different types, and different number of parameters is not supported by TypeScript.

12. What does the TypeScript keyword declare?

Answer: The TypeScript keyword declares that instructs the compiler not to trans-compile the code into JavaScript as it exists in external code.

13. What is a TypeScript Map File?

Answer: The Map TypeScript file converts the trans-compiled JavaScript from an unreadable format to a format that is understandable by humans. Since the source map will be used, this is beneficial if debugging is required during production.

14. In TypeScript, what is a compiler reference?

Answer: When TypeScript code is built, your compiler will inspect the collection of files and parse them to find out which code is acceptable and which is invalid. However, TypeScript also gives you the opportunity to modify the compiler settings, and this is done using the tsconfig.json file.

15. What are TypeScript’s access modifiers?

Answer: When interacting with class members, TypeScript uses several access modifiers. The public, private and protected modifiers are those that are supported.

These tasks are as follows:

  1. Being public means that the instance of a class, the child class and all its members can access it.
  2. Private means that the members of a class are separate from each other.
  3. An instance of a class cannot access a resource that all its members, including its descendant classes, can access.

It is assumed that a class member is public if the access modifier for that member is left unspecified. Wherever possible, you should explicitly specify access as this can lead to problems with compliance processes.

You should also be aware that once your TypeScript code is created, the class modifier has no effect. These modifiers are not taken into account when the compiler generates the resulting JS.

16. Is JSX compatible with TypeScript?

Answer: It is possible However, you must save your TypeScript file with the a.tsx extension.

But when working with JSX and TypeScript, there are several important things to remember. JSX has to be compiled into valid JS because it is an embeddable XML-like syntax. This increases the number of compilation steps in your code, which can have an impact on performance.

On the other hand, TypeScript provides a number of robust tools for working with JSX, including type validation, embedding, and direct JSX compilation.

17. What do TypeScript triple-slash instructions do?

Answer: In TypeScript, triple-slash instructions and functions are similar to comments in that they both carry compiler instructions. These consist of single XML tags.

Triple-slash instructions work only when they are at the top of the contained file. However, if they are followed by another type statement or declaration, your compiler will treat them as standard comments and ignore them. You can place comments in front of them, including additional triple-slash instructions.

18. What are the JSX modes compatible with TypeScript?

Answer: There are three JSX modes included with TypeScript by default. These react native, react and protected.

The JSX output of your code can be customized using these settings. The goal of Protected Mode is to keep the JSX output within your compiled code so that another compiler can operate on it directly.

When this mode is activated the compiler will create a file with the .jsx file extension so that it can be further modified before use. Similar functionality is provided by react-native method. However, the output is given a .js file extension.

React mode works a little differently because it omits the React.createElement modifier, the result being devoid of raw JSX code. When using this mode, the output file will have a .js file extension.

19. What do TypeScript decorators do?

Answer: In these last few questions we will discuss some of the more distinctive features of TypeScript. These characteristics will be brought up again and again during the interview because knowing about them shows that you have used them frequently.

“Decorator” is the first of these features. A specific type of declaration called a decorator is used to supplement existing code with annotations and metadata. They take declarative action. You must enable them in order to use the experimental decorators compiler functions.

20) What do the rest parameters of TypeScript mean?

Answer: The rest parameter, a unique parameter that enables you to pass a value to a function, is also a feature of TypeScript. You can call this, by putting an ellipsis (…) before the parameter you are working with. This makes it possible for functions to work with different arguments, which is very useful if you need to supply a function with an unknown amount of parameters.

However, there are a few things to keep in mind when using the rest parameter:

  1. For each function, only one rest parameter can be used.
  2. An array type must be explicitly defined.
  3. It needs to be as the last argument in the parameter list.

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