List of the 20 Most Important TypeScript Interview Questions of 2023

When being interviewed for a job that requires TypeScript experience, it is likely that you will face questions related to the language itself. These queries could include asking about object-oriented notation that TypeScript recognises or the notable differentiators between TypeScript and JavaScript. It is advantageous to be able to answer these questions as it allows the candidate to display their understanding of TypeScript and helps to evaluate their knowledge of the language.

Looking for solutions to these problems? Keep reading.

Define what TypeScript is.

TypeScript is a programming language that is a strict syntactical superset of JavaScript. It enables developers to write bigger applications while opting for optional static typing and then compiles the code to JavaScript. The usage of TypeScript enhances the readability, scalability, and maintainability of the code.

TypeScript source code is typically saved using “.ts” as the file extension. Once the code is written, the TypeScript compiler is utilised to generate the corresponding JavaScript code. Any text editor can be used to create these files. However, to use TypeScript code, you must have the compiler installed on your platform. To compile the code, “tsc .ts” can be used as a command. For instance, one can utilise “tsc myScript.ts”.

Greetings to Works!
Let’s set up a variable message using TypeScript:
var message:string = “Welcome!”

Print the value of the variable message using:
console.log(message)

Easy interview questions based on TypeScript

1. What benefits does TypeScript provide while developing applications?

   The following are some of the advantages of using TypeScript during application development:
   1. TypeScript is speedy, simple to comprehend, and runs quickly. Additionally, it can be executed in any browser or JavaScript engine.
   2. The syntax and semantics of TypeScript are identical to JavaScript. This means that developers can create front-end code more quickly. This accelerates the development process.
   3. TypeScript is also compatible with existing JavaScript frameworks and libraries.
   4. The usage of a Definition file (which ends in.d.ts) allows you to use established JavaScript libraries such as Jquery, D3.js, and more.
   5. TypeScript’s ES6 and ES7 features can work in collaboration with JavaScript ES5 engines. This enables you to utilise it with tools such as Node.js.

2. What are the drawbacks of using TypeScript?

   Here are some of the limitations associated with TypeScript:
   1. TypeScript has a lengthy compilation time due to its intricate syntax.
   2. You cannot create an abstract class with TypeScript.
   3. To run a TypeScript program in a browser, you must first compile the TypeScript code to JavaScript.
   4. A library definition file has to be present before you can utilise any external library.
   5. The quality of the type definition files is low.

3. What are the Major Components of TypeScript?

   TypeScript is a programming language that is made up of three significant components. These components can be viewed as separate layers, with their individual code snippets that can be used. The three main components of TypeScript are: static type checking, class-based object-oriented programming, and a refined type system. Static type checking is a procedure of verifying the precision of the data types used in code. Class-based object-oriented programming enables you to create classes and objects for better organisation of your code and ease of maintenance. The refined type system in TypeScript enables more detailed and efficient programming by allowing for type inference and aliasing. Each component adds distinct advantages for developers who use TypeScript.
   1. Language
   2. The Process of Using the TypeScript Compiler
   3. Supported Languages for TypeScript

4. Explain the Functionality and Attributes of Arrays in TypeScript.

   Some of the distinct characteristics of TypeScript’s Arrays are mentioned below.
   1. You cannot alter an array. This suggests that once an array has been established, its size cannot be modified.
   2. For instance, the components of an array are saved in separate memory blocks.
   3. The index or subscript of an element in the array is a distinctive numerical identifier.
   4. Before an array can be utilised, it must be defined by using the ‘var’ keyword. Following this, the array can be operated in the same manner as a variable.
   5. When information is inserted into an array, it is referred to as being “initialised for the first time.”

5. What is the Appropriate Location for TypeScript Variable Declarations?

   In order to declare a variable, either the `let` or `const` statements must be employed. The utilisation of both these declarations is essential for correctly declaring the variable. Moreover, the conditions specified below must be satisfied to ensure that the declaration is valid.
   1. Variable names must comprise solely of alphanumeric characters and integers.
   2. With the exception of the underscore (_) and the dollar sign ($), variable names cannot include spaces or other non-alphanumeric characters.
   3. A variable name cannot start with a numeric value.
      
      Syntax example:
      The variable ‘an’ is assigned the value of 10;
      or
      Utilising f()
      Hello, Works! Variable message =;
      message back;
      }

6. What Types of Access Modifiers are Acknowledged by TypeScript?

   The following access modifiers are approved by TypeScript:
   1. Access Modifier for Secure Access
   2. Modification for Confidential Use Only
   3. An Access Modifier for Open Access

7. In Typescript, How are Loop Statements Defined?

   A loop statement allows code to be executed repeatedly. TypeScript provides a multitude of looping options to fulfil various looping needs, including but not limited to those presented below.
   1. In Regard to the Loop:
   2. As long as the iteration is within the While Loop
   3. The Do…While Looping Structure

8. What is the Definition of Static Typing?

   Static typing allows a compiler to recognise variables, arguments, and object members during compilation. With Static Typing, programming errors can be identified and corrected before they cause significant problems.

9. Is TypeScript suitable for backend development?

   Absolutely. TypeScript’s added security is a significant advantage for Node.js backend applications.

10. How do you check if a TypeScript variable is undefined or not?

    The if (value) statement will return true if the value is not null, undefined, empty, false, 0 or NaN.

Potential Questions for an In-Depth TypeScript Interview

1. What is the meaning of “type assertion”?

   TypeScript utilises type assertions to clearly indicate to the compiler the data type of a specific value. This ensures that the compiler does not perform any additional data restructuring or validation. This type of assertion does not have any impact on code performance and is solely used to provide the compiler with essential information. It is the responsibility of the programmer to perform any necessary checks before making use of the assertion.

2. What are Recursive Type Aliases?

   Due to the requirement that each alias type must act as a direct substitute for its aliases’ targets, using Type Aliases in a recursive manner was not typically feasible. As a result, recursive aliases are not accepted by the compiler because they are not always possible.
   
   While type aliases cannot be recursive, interfaces can be, though with somewhat limited capability. This is accomplished by taking the process of creating a type alias and breaking down its recursive components as interfaces.
   
   Here is an example syntax:
   type ValueOrArrayT> = T | ArrayOfValueOrArrayT>;
   The ArrayValueOrArrayT> interface inherits from ArrayValueOrArrayT>>

3. How can one easily obtain “declaration” files?

   The declaration compiler option in the tsconfig.json file must be set to true. This can be accomplished by modifying the values in the “compilerOptions” like so:
   {
   …”compilerOptions”: {
   …”declaration”: true,
   …
   }
   …
   }

4. How can a function be overridden?

   To override, use the same function name directly above the original function, this time without brackets. Modify the input and output types as well as the number of parameters according to your requirements.
   
   An example would be as follows:
   string function add(string x, string y);
   The add(x, y) method returns a larger value if x > y.
   revert x + y;
   }

5. What are TypeScript Modules?

   TypeScript code can be modularised using modules. There are two primary types of modules. Some of them are listed below:
   

   1. Internal Modules:

      In previous versions of TypeScript, classes, interfaces and functions were usually grouped together in “internal modules” before being exported to another module. In the TypeScript environment, this type of organizational structure is now referred to as a “namespace”.

   2. Add-Ons and Adapters:

      Developers working with TypeScript can utilise external modules to define and load interdependencies between various external JavaScript scripts.

6. How can all properties of an interface be made optional?

   By using the “Partial” mapped type, programmers can transform any property of an interface into a purely optional one.
   
   Here is an example syntax:
   interface Person {
   name: string;
   age: number;
   }
   type PartialPerson = Partial; // As shown below
   The PartialPerson interface
   name: string | undefined;
   age?: number | undefined;
   }

7. Where can decorators be used?

   Decorators can be applied to classes, properties, methods and method arguments.
   
   For example:
   @MyClassDecorator
   import Person
   …
   @MyPropertyDecorator string; myProperty;
   }

8. What is the purpose of the “Record” library?

   The “Record” library allows programmers to create a typed, programmable map.
   
   For example:
   let Person = Record = {};
   Person.Age = 20;

9. How can one use classes that are not included in a particular module?

   To use a class that is not part of a module, the “export” keyword must be used before the class name.
   
   For example:
   import Person

10. Firstly, what are Distributive Conditional Types?

    The checked type parameter in conditional and distributive conditional type declarations is a basic type parameter. When instantiated, the distributive conditional types become evenly distributed across the various union types.
    
    Instances of T extends U? X: Y are resolved as (A extends U? X: Y) | (B extends U? X: Y) | (C extends U? X: Y).

How can one best prepare for TypeScript-related queries?

It’s important to note that TypeScript is a high-quality front-end web development tool because of its strong support for JavaScript.

As a result, it is expected that the interview questions will mainly centre on topics related to front-end development, such as HTML, CSS, responsive design, frameworks, version control, web performance, user interface, and more. Additionally, the interview may cover key aspects of TypeScript, including classes, components, arrays, functions, modules, interfaces, and generic and static typing.

To gain a better understanding of the topics discussed, it is advisable for learners to take the time to explore and practice the ideas and concepts presented. Moreover, the suggested questions can serve as a valuable review guide. For those who want to expand their knowledge, there are several free online coding environments that offer opportunities to gain practical experience and see how these concepts can be implemented in real-world scenarios.

If you are seeking a chance to land a well-paying job in the United States, Works might be the solution for you. Works provides lucrative, long-term software engineering opportunities that can be done remotely.

FAQs

1. What object-oriented notations are supported by TypeScript?

   The following object-oriented notations are recognised by TypeScript:
   1. Modules
   2. Classes
   3. Interfaces
   4. Inheritance
   5. Data Formats:
   6. Roles of Participants:

2. What are the main differences between TypeScript and JavaScript?

   TypeScript is an object-oriented programming language that was designed to be an alternative to the existing online programming language JavaScript. While JavaScript is mainly used for creating dynamic web pages, TypeScript is an open-source language that is especially suitable for building complex web applications.