Typescript Interview Questions & Answers [BEST & NEW] - 2020
TypeScript Interview Questions and Answers

Typescript Interview Questions & Answers [BEST & NEW]

Last updated on 04th Jul 2020, Blog, Interview Questions

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TypeScript is a superset of JavaScript that adds static typing to the language. It allows developers to define explicit types for variables, functions, and other constructs, enhancing code reliability and maintainability. TypeScript code is transpiled into standard JavaScript, making it compatible with any JavaScript runtime. It offers features like interfaces, classes, and advanced type annotations, making it particularly useful for large-scale applications where strong typing can help catch errors early in the development process.

1. What is Typescript?

Ans:

TypeScript is a superset of JavaScript that adds static typing and other features to the language.TypeScript is a programming language developed by Microsoft. It is a superset of JavaScript, meaning that it includes all JavaScript features and adds static typing to enhance code quality and maintainability. TypeScript code eventually transpired into JavaScript, making it compatible with any JavaScript runtime.

 2. What is the purpose of static typing in TypeScript?

Ans:

Static typing helps catch type-related errors during development, before runtime, providing better code reliability. The purpose of static typing in TypeScript is to catch potential errors during development by enforcing variable types at compile time. This helps in identifying and fixing issues early in the development process, enhancing code reliability and maintainability. Static typing also provides better code documentation, as developers can explicitly define the expected types of variables, making the codebase more understandable.

3. How do you define a variable with a specific type in TypeScript?

Ans:

In TypeScript, you can define a variable with a specific type using the colon (:) syntax after the variable name.

You use the colon (:) syntax to declare the type, like this: let myVar: number = 10;

4. What are interfaces in TypeScript?

Ans:

Interfaces define a contract for object shapes, specifying the properties and their types. They help achieve better code organization and maintainability. Interfaces in TypeScript define the structure of an object by specifying the expected properties and their types. They act as a blueprint for creating objects with consistent shapes.

 5. Explain the benefits of using TypeScript.

Ans:

  • Static Typing: Catches errors early, improving code reliability.
  • Tooling Support: Enhances productivity with features like autocompletion.
  • Readability: Type annotations improve code clarity.
  • Code Quality: Early issue detection leads to higher quality.
  • ECMAScript Compatibility: Seamlessly integrates with JavaScript.
  • Community & Ecosystem: Thriving community and rich toolset.

6. Explain the difference between null and undefined in TypeScript.

Ans:

  • Null is a value that represents the intentional absence of any object value. It is a valid value of the null type.
  • Undefined is a value usually assigned to a variable that has not been initialized or to a function parameter that lacks an argument. It is a valid value of the undefined type.
  • Both represent the absence of a value, but null is a value that has been explicitly set, while undefined usually indicates an uninitialized or missing value.

7. How can you use generics in TypeScript?

Ans:

  • In TypeScript, generics allow you to create reusable components that can work with various data types.
  • You can use generics by defining type parameters within angle brackets < >
  • Generics allow you to write functions or classes that can work with different data types. You declare generics using angle brackets (<>).

8. What is the purpose of the tslint.json file in a TypeScript project?

Ans:

tslint.json configures TSLint, a static analysis tool for TypeScript, enabling you to define and enforce coding standards and best practices. The tslint.json file in a TypeScript project is used to configure TSLint, a static analysis tool for TypeScript code. It defines rules and configurations to enforce coding standards, style guidelines, and other code quality aspects within the TypeScript codebase.

9. Explain the concept of type inference in TypeScript.

Ans:

 Type inference is TypeScript’s ability to automatically determine the type of a variable based on its initialization. This helps reduce the need for explicit type annotations. Type inference in TypeScript is the compiler’s ability to automatically deduce and assign types to variables based on the values assigned to them. TypeScript uses the static analysis of the code to analyze variable assignments, function return types, and other contextual information to infer the types without explicit annotations.

10. How can you achieve inheritance in TypeScript?

Ans:

Use the extends keyword to create a subclass that inherits from a base class in TypeScript.Inheritance is accomplished using the extends keyword. A class can extend another class to inherit its properties and methods.

11. How do you handle asynchronous operations in TypeScript?

Ans:

TypeScript supports asynchronous programming using Promises, async/await syntax, and other patterns. Asynchronous operations are commonly used with functions returning promises. In TypeScript, you can handle asynchronous operations using Promises, async/await syntax, or callbacks. Promises provide a clean way to work with asynchronous code, and async/await syntax makes it even more readable.

12. What is the difference between let, const, and var in TypeScript?

Ans:

  • Var has function-scoping, is hoisted, and can be redeclared.
  • Let has block-scoping, is not hoisted, and can be reassigned.
  • Const has block-scoping, is not hoisted, and cannot be reassigned (immutable).

13. What is any type in TypeScript, and when should you use it?

Ans:

  • Any type is used to represent values for which you do not know or care about the type.
  • It should be used sparingly, as it sacrifices the benefits of static typing. In TypeScript, any type is a flexible type that can represent any value.
  • It turns off type-checking for a particular variable, allowing it to hold values of any type without TypeScript raising type-related errors.

14. Explain the concept of modules in TypeScript.

Ans:

Modules in TypeScript provide a way to organize code. You can use the export and import keywords to control the visibility of classes, functions, or variables across files. In TypeScript, modules are a way to organize and encapsulate code. They allow you to split your code into smaller, reusable pieces, making it easier to manage and maintain large projects.

15. How does TypeScript support optional and default function parameters?

Ans:

In TypeScript, you can make function parameters optional by appending a question mark to their names. For default values, you use the assignment operator = to provide a fallback if no value is provided. You can make function parameters optional by adding a ? after the parameter name. Default parameters are specified with the assignment operator (=) after the parameter declaration.

16. What is the purpose of decorators in TypeScript?

Ans:

Decorators provide a way to modify or annotate classes and class members. They are often used in frameworks like Angular for metadata and behaviour extension. In TypeScript, decorators are used to annotate and modify classes or class members (methods, properties, etc.). They provide a way to extend or modify the behaviour of classes at design time. Decorators are commonly used in frameworks like Angular for features like dependency injection and component metadata.

17. How is TypeScript different from JavaScript?

Ans:

  Feature TypeScript JavaScript
Type System Supports static typing with optional type annotations, allowing developers to define types for variables, function parameters, and return values A Dynamically typed language that allows for flexibility but may result in runtime errors because types are inferred at runtime
Tooling Support Provides rich tooling support including IDE integration, code completion, static analysis, and refactoring tools, thanks to TypeScript’s strong typing and static analysis capabilities Tooling support varies among different IDEs and editors, with limited support for static analysis and code completion due to dynamic typing
Compilation Requires compilation step to convert TypeScript code to JavaScript code, typically using the TypeScript compiler (tsc) Written directly in JavaScript and executed by browsers or JavaScript engines without the need for compilation
Code Readability Enhances code readability and maintainability by allowing developers to express their intent through type annotations and clearer code structure May require additional documentation or comments to convey the intended types or behavior of variables and functions
Error Checking Offers compile-time error checking to catch type-related errors and issues before runtime, reducing the likelihood of runtime errors Relies on runtime error checking, which may lead to unexpected behavior or errors that are only discovered during execution

18. How can you configure TypeScript to target a specific ECMAScript version?

Ans:

Configure TypeScript to target a specific ECMAScript version by using the –target compiler option in your tsconfig.json file. The target option in tsconfig.json allows you to specify the ECMAScript version your TypeScript code should be transpiled to, such as ES5, ES6, etc.

19. Explain the concept of union types in TypeScript.

Ans:

 Union types allow a variable to hold values of multiple types. You use the | operator to define a union, like this: let myVar: number | string. In TypeScript, union types allow a variable to have multiple types. This means a variable can be of one type OR another. define a union type using the pipe (|) symbol. For example, number | string denotes a variable that can be either a number or a string. This flexibility is useful when a function or variable can work with different types.

20. How does TypeScript handle null and undefined types by default?

Ans:

 By default, TypeScript has the strictNullChecks option enabled, which means you need to explicitly specify null or undefined in a variable’s type union to allow these values. In TypeScript, by default, variables can have values of null or undefined unless you specify otherwise. This is due to the language’s optional static typing. To make a variable not accept null or undefined, you can use strict null checks by enabling the –strictNullChecks compiler option. This helps catch potential issues related to null and undefined values during development.

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    21. What is the role of the tsconfig.json file in a TypeScript project?

    Ans:

    tsconfig.json configures the TypeScript compiler, specifying compiler options, file inclusion/exclusion, and other project settings. The tsconfig.json file in a TypeScript project serves as a configuration file that defines various settings and options for the TypeScript compiler (cc). Its primary role is to manage how TypeScript files are compiled into JavaScript and to specify the project’s compilation settings.

    22. What are the key differences between interface and type in TypeScript?

    Ans:

    Syntax:

    • Interface: Declared with interface.
    • Type: Declared with type.

    Extending/Implementing:

    • Interface: Uses extends for extension.
    • Type: Creates new types by combining existing ones.

    Declaration Merging:

    • Interface: Supports declaration merging.
    • Type: Doesn’t support declaration merging.

    Compatibility with Primitives:

    • Interface: Compatible with primitives.
    • Type: More versatile with union types and mapped types.

    23. How can you implement private and protected members in a TypeScript class?

    Ans:

    Private Members:

    • Use the private keyword before a member.
    • Example: private variableName: string;

    Protected Members:

    • Use the protected keyword before a member.
    • Example: protected methodName() { }

    24. What is the purpose of the readonly modifier in TypeScript?

    Ans:

    Read-only is used to make properties or array elements immutable. Once a property is marked as read-only, it cannot be reassigned. The read-only modifier in TypeScript is used to indicate that a property or variable should not be modified after it’s been initialized. It ensures that the value assigned to the property or variable remains constant throughout its lifetime. This is particularly useful when you want to define constants or ensure immutability in certain parts of your code. Once a property or variable is marked as read-only, attempting to reassign a value to it will result in a compilation error.

    25. How can you create and use type aliases in TypeScript?

    Ans:

    In TypeScript, you can create type aliases using the type keyword. Type aliases use the type keyword and allow you to create a name for a specific type.

    For example type MyAlias = string | number;

    26. Explain the concept of ambient declarations in TypeScript.

    Ans:

    Ambient declarations are used to tell TypeScript about variables and types that exist in external code (like JavaScript libraries) but are not explicitly defined in TypeScript.Ambient declarations in TypeScript are used to declare the shape of external entities, typically those provided by JavaScript libraries or environments that don’t have TypeScript type definitions. They allow you to provide type information for code that exists outside the TypeScript project, enhancing the compatibility and development experience.

    27. What is the purpose of the –strict flag in TypeScript?

    Ans:

    • The –strict flag is a shorthand to enable a set of strict type-checking options in TypeScript, including noImplicitAny, strictNullChecks, and others.
    • The –strict flag in TypeScript enables a strict set of type-checking options. It includes flags like –noImplicitAny, –strictNullChecks, –strictFunctionTypes, and others.
    • Enabling –strict helps catch more potential errors during development by enforcing stricter type rules.

    28. How do you use TypeScript with React?

    Ans:

    Install TypeScript: npm install –save typescript @types/node @types/react @types/react-dom.

    • Create tsconfig.json: npx tsc –init.
    • Rename files to .tsx.
    • Add type annotations to components, props, and states.
    • Use TypeScript with React hooks, providing types.

    29. What is the triple-slash directive in TypeScript?

    Ans:

    Triple-slash directives are special comments used to include reference files, such as declaration files or other dependencies. They begin with ///. The triple-slash directive in TypeScript is a way to include reference path comments for the TypeScript compiler. It’s primarily used in declaration files (.d.ts) to reference other declaration files or dependencies.

    30. How can you configure TypeScript to compile all TypeScript files in a project?

    Ans:

    Can use the –project or -p flag followed by the path to the directory containing the tsconfig.json file to compile all TypeScript files in a project. You can configure TypeScript to compile all TypeScript files in a project by creating a tsconfig.json file at the root of your project. Set the “include” property to include the file patterns you want to compile

    31. What is the purpose of never typing in TypeScript?

    Ans:

    The never type represents values that never occur. It is often used as the return type for functions that throw exceptions or enter infinite loops. In TypeScript, the never type represents values that never occur. It is often used in situations where a function cannot return or a variable cannot have any possible value. For example, a function that always throws an error or enters an infinite loop would have a return type of never. It helps in catching unintended code paths and improving type safety in your TypeScript code.

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    33. Explain the concept of Enums in TypeScript.

    Ans:

    Enums allow you to define a set of named constants, making it easier to work with a set of related values. For example: enum Color { Red, Green, Blue }.In TypeScript, Enums, short for enumerations, allow you to define a set of named constants. These constants can represent a set of related values, making your code more readable and maintainable. Enums are defined using the enum keyword.

    34. What is the purpose of the –esModuleInterop compiler option in TypeScript?

    Ans:

    • This option simplifies interoperability between CommonJS and ES modules by enabling a more seamless import/export experience.
    • The –esModuleInterop compiler option in TypeScript is used to simplify interoperability between TypeScript modules (which follow the ECMAScript Module syntax) and CommonJS modules (which use required syntax).
    • When this option is set to true, TypeScript allows more flexible import patterns, making it easier to work with modules that were originally designed for CommonJS.

    35. Explain the difference between ambient modules and external modules in TypeScript.

    Ans:

    • Ambient modules use the declare module syntax to describe the shape of an external module.
    • External modules use the module keyword and are typically used with external dependencies.
    • In TypeScript, the terms “ambient modules” and “external modules” have been largely replaced by the more general concepts of “declaration spaces” and “modules.

    36. How does TypeScript handle type assertions?

    Ans:

    Type assertions allow you to tell the TypeScript compiler that you know more about the type of a value than it does. They are performed using the keyword or the <Type> syntax. In TypeScript, type assertions are a way for you to tell the compiler that you know more about the type of a value than it does. It’s like a typecast in other languages.

    37. What is the –strictBindCallApply option in TypeScript?

    Ans:

    This option enforces stricter rules for bind, call, and apply methods, providing better type-checking for function calls. The –strictBindCallApply option in TypeScript enables stricter checking for the bind, call, and apply methods on functions. When enabled, TypeScript checks that the target function’s parameters match the provided arguments in these function calls. This helps catch potential errors where incorrect arguments are passed during function invocation using these methods.

    38. How can you use TypeScript with third-party JavaScript libraries?

    Ans:

    Can use declaration files (.d.ts) to provide type information for existing JavaScript libraries, allowing TypeScript to understand their APIs.To use TypeScript with third-party JavaScript libraries, you need to obtain or write type declarations for those libraries. Type declarations provide information about the types used in the JavaScript code, enabling TypeScript to perform type-checking.

    39. What is the purpose of the read-only array in TypeScript?

    Ans:

    In TypeScript, the read-only modifier is used to create read-only versions of array types. When you declare an array as read-only, it means that once the array is created, you cannot modify its contents. This helps prevent unintentional modifications and enhances the immutability of data structures. The read-only array ensures that once an array is initialized, its elements cannot be modified. This is different from const arrays, which can still be reassigned.

    40. How can you achieve conditional types in TypeScript?

    Ans:

    Conditional types use the extends keyword to choose between two types based on a boolean condition conditionally. For example: type MyType<T> = T extends string? True: false; Conditional types in TypeScript allow you to create types that depend on other types. You can achieve this using the extends keyword within a type definition.

    41. Explain the purpose of the –strictFunctionTypes compiler option in TypeScript.

    Ans:

    • –strictFunctionTypes enforces stricter checking on function parameter types, making sure function parameters are contravariant with their declared types.
    • The –strictFunctionTypes compiler option in TypeScript enforces strict checking of function types during assignment.
    • When enabled, it ensures that function parameter types are contravariant for function arguments and covariant for return types.
    • This helps catch potential errors related to function type compatibility, promoting stricter type checking and reducing the risk of unintended type assignments in your code.

    42. How can you use TypeScript with Node.js?

    Ans:

    • Install TypeScript globally: npm install -g typescript.
    • Initialize TypeScript project: tsc –init
    • Write TypeScript code (.ts files).
    • Install Node.js typings: npm install –save-dev @types/node.
    • Compile TypeScript: tsc (generates JavaScript in a dist folder)
    • Run with Node.js: node dist/yourFile.js

    43. What is the key operator in TypeScript?

    Ans:

    Key of is a TypeScript operator that produces a union type of string literals representing the keys of an object type. It allows you to capture the keys of an object as a type, providing type safety when working with object properties. The key of the operator is used to obtain the keys of an object type. For example, type MyKeys = key of { name: ‘John’, age: 30 }; results in ‘name’ | ‘age’.

    44. Explain the concept of mapped types in TypeScript.

    Ans:

    Mapped types in TypeScript allow you to create new types by transforming the properties of an existing type. The keyword and keyword are often used in combination with mapped types. Mapped types allow you to create new types based on existing ones by transforming each property. For example: type Optional<T> = { [K in keyof T]?: T[K] };.

    45. How can you use TypeScript with Webpack?

    Ans:

    TypeScript can be integrated with Webpack by configuring a tsconfig.json file, installing the necessary loaders (ts-loader), and specifying TypeScript as the compiler in the Webpack configuration.

    46. How does TypeScript handle type inference for generics?

    Ans:

    TypeScript uses a mechanism called “type inference” to automatically determine and assign types based on the values used. For generics, TypeScript infers types by examining the provided arguments when a generic function or class is called.TypeScript uses type inference to automatically determine the generic type based on the provided arguments, reducing the need for explicit type annotations.

    47. What is the purpose of the –skipLibCheck compiler option in TypeScript?

    Ans:

    The –skipLibCheck compiler option in TypeScript allows you to skip type checking of declaration files (*.d.ts). It can be useful when working with third-party libraries that may have incomplete or incorrect type definitions. Skipping type checking for declaration files can speed up the compilation process and avoid unnecessary errors related to external library typings.

    However, using this option means you might miss potential type-related issues in your code when interacting with those libraries. –skipLibCheck skips type-checking of declaration files (.d.ts), which can be useful to speed up the compilation process when using large third-party libraries.

    48. Explain the purpose of the –declaration compiler option in TypeScript.

    Ans:

    • The –declaration compiler option in TypeScript is used to generate corresponding “.d.ts” (declaration) files during the compilation process.
    • These declaration files contain type information for the TypeScript code, allowing developers to use TypeScript in conjunction with JavaScript libraries or frameworks.
    • –declaration generates declaration files (.d.ts) alongside the compiled JavaScript files, providing type information for consumers of the TypeScript code.

    49. What is the purpose of the readonly modifier for array types in TypeScript?

    Ans:

    • In TypeScript, the read-only modifier for array types ensures that once an array is assigned, its elements cannot be modified.
    • This helps prevent accidental or intentional changes to the array’s content after initialization, promoting immutability and enhancing code safety.
    • The read-only modifier for array types ensures that the array itself cannot be reassigned and its length cannot be modified after initialization.

    50. What is the purpose of the export = syntax in TypeScript?

    Ans:

    • The export = syntax is used for creating external modules in TypeScript. It allows a module to be consumed using the import = require() syntax.
    • In TypeScript, the export = syntax is used for module exports. It allows you to export a single value (class, function, etc.) from a module as the default export.
    • This syntax is commonly used in scenarios where a module needs to provide a single primary entity for other modules to import.

    51. What are conditional module imports in TypeScript?

    Ans:

    Conditional module imports in TypeScript allow you to import modules based on certain conditions. This is useful when you want to load modules dynamically depending on runtime conditions. You can achieve this using TypeScript’s import() syntax, which returns a Promise for the module. Conditional module imports allow you to import a module based on a condition. TypeScript supports dynamic import() expressions for this purpose.

    52. How can you handle type assertions with TypeScript and JSX?

    Ans:

     In JSX, type assertions are done using the keyword. For example: <div>{(some variable as string).toUpperCase()}</div>In TypeScript and JSX, you can use type assertions to inform the compiler about the actual type of a value when the type checker is unable to infer it correctly.

    53. How does TypeScript support mixing patterns?

    Ans:

    In TypeScript, mixing patterns are supported through a combination of features like intersection types, generics, and utility types. You can create reusable components with specific functionality and then combine them using intersection types to form a new type with the combined features.TypeScript supports mixins by combining multiple classes or objects to create a new class with the merged functionality.

    54. How can you use TypeScript with React hooks?

    Ans:

    • Install TypeScript and @types/react: npm install –save typescript @types/react @types/react-dom
    • Create tsconfig.json: Basic setup for TypeScript configuration.
    • Rename your .js files to .tsx: Use the TypeScript extension for React files.
    • Add TypeScript to functional components: Specify types for props and state.
    • Use useState and useEffect hooks: Annotate state types and effect dependencies.
    • Use generic types for useState: Enhance type inference for the state.
    • Leverage custom hooks: Type custom hooks for reuse across components.
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    55. Explain the role of the never type in function return types.

    Ans:

    The never type in function return types indicates that the function will never return a value, usually used for functions that throw errors or enter infinite loops. The never type in TypeScript represents a value that never occurs. It’s often used in function return types to indicate that the function will never return normally, either because it throws an exception or enters into an infinite loop.

    56. What is the purpose of the export = syntax in TypeScript?

    Ans:

     The export = syntax is used for creating external modules in TypeScript. It allows a module to be consumed using the import = require() syntax. In TypeScript, the export = syntax is used for module exports. It allows you to export a single value (class, function, etc.) from a module as the default export. This syntax is commonly used in scenarios where a module needs to provide a single primary entity for other modules to import.

    57. How can you use TypeScript with asynchronous code and Promises?

    Ans:

    TypeScript supports asynchronous code through Promises, async/await syntax, and the Promise type for handling asynchronous operations. In TypeScript, you can use asynchronous code and Promises by leveraging the async/await syntax. When defining a function that involves asynchronous operations, mark it with the async keyword. Use the await keyword to wait for a Promise to resolve.

    58. What is the purpose of the –isolatedModules compiler option in TypeScript?

    Ans:

    • The –isolated modules compiler option in TypeScript ensures that each file is treated as a separate module.
    • This can help catch certain errors related to module dependencies and promote better modularization in your code.
    • –isolated modules ensure that each file is treated as an isolated module, preventing unintended sharing of variables across files and promoting better encapsulation.

    59. How does TypeScript handle optional chaining?

    Ans:

    • TypeScript supports optional chaining with the (?. )Syntax. It allows you to safely access properties or call methods on an object, even if some intermediate properties are null or undefined.
    • If any part of the chain is null or undefined, the entire chain is evaluated to be undefined. This helps prevent runtime errors caused by attempting to access properties on null or undefined values.
    • Optional chaining (?.) allows you to access properties or call methods on nested objects without worrying about null or undefined values, providing a more concise and safe syntax.

    60. What are namespace imports in TypeScript?

    Ans:

    Namespace imports allow you to import an entire module as an object, providing a way to organize and access multiple exported values. In TypeScript, namespace imports allow you to bring in types, interfaces, functions, or variables from one namespace into another. This is done using the import keyword followed by the * as alias syntax.

    61. How does TypeScript handle this keyword in functions?

    Ans:

    TypeScript supports specifying the type of this for functions using function signatures or arrow functions, providing better type checking for this context. In TypeScript, this keyword behaves similarly to JavaScript. However, TypeScript provides better support for handling this context through explicit type annotations or arrow functions.

    62. Explain the purpose of the –strictPropertyInitialization compiler option.

    Ans:

    • –strictPropertyInitialization ensures that class properties are initialized in the constructor or through definite assignment assertions, reducing the risk of uninitialized properties.
    • The –strictPropertyInitialization compiler option in TypeScript enforces stricter rules for initializing class properties.
    • It helps catch potential bugs related to uninitialized properties by ensuring that all non-optional properties are initialized in the constructor or through property assignments.

    63. How can you use decorators with class expressions in TypeScript?

    Ans:

    In TypeScript, you can use decorators with class expressions by applying the decorator directly to the class declaration. Decorators can be applied to class expressions using the @expression syntax, allowing dynamic behavior based on the class expression.

    64. What is the import type syntax in TypeScript?

    Ans:

    In TypeScript, you can use the import statement to bring in functionalities from other modules. The import type syntax is used to import only the type information of a module, excluding the runtime values. This can be useful for reducing runtime dependencies.

    65. What are abstract classes in TypeScript, and how are they different from regular classes?

    Ans:

    In TypeScript, abstract classes are used as base classes that cannot be instantiated on their own. They may contain abstract methods, which are declared but not implemented in the abstract class. Subclasses extending an abstract class must provide concrete implementations for these abstract methods. Abstract classes cannot be instantiated directly and are meant to be subclassed. They can contain abstract methods, which their derived classes must implement.

    66. How can you use this parameter in TypeScript functions?

    Ans:

    In TypeScript, this parameter is used to specify the type of context within a function. You can use it as the first parameter in a function declaration. This parameter allows you to explicitly specify the type of this in a function, providing better type checking and documentation for the function’s intended use.

    67. How does TypeScript handle function overloading?

    Ans:

    • In TypeScript, function overloading allows you to define multiple function signatures for the same function name.
    • TypeScript uses these signatures to check and enforce the correct usage of the function.
    • TypeScript supports function overloading by allowing you to provide multiple type signatures for a function, each specifying different parameters and return types.

    68. What is the role of the infer keyword in TypeScript conditional types?

    Ans:

    • The infer keyword in TypeScript is used within conditional types to declare a type parameter that will be inferred by the compiler when the conditional type is instantiated.
    • It allows you to capture and use the type of a specific expression or type within the true or false branch of a conditional type.
    • The infer keyword is used in conditional types to introduce a type variable, allowing the assignment of a type to be used elsewhere in the conditional type.

    69. Explain the concept of type guards in TypeScript.

    Ans:

    In TypeScript, type guards are a way to narrow down the type of a variable within a certain block of code. They help TypeScript understand more specific types based on runtime checks. For example, using typeof, instanceof, or custom user-defined functions, you can create type guards. Type guards are expressions or functions that help narrow down the type of a variable within a certain code block, improving TypeScript’s understanding of types.

    70. How does TypeScript handle discriminated unions for improved type narrowing?

    Ans:

    TypeScript uses discriminated unions, also known as tagged unions or algebraic data types, to improve type narrowing. A discriminated union is a union type where each member has a common property, known as a discriminant. This discriminant property allows TypeScript to narrow down the type within the union based on that property. Discriminated unions use a common property in the type to determine the actual type, allowing TypeScript to narrow down the type based on that property.

    71. What is the purpose of the import() syntax in TypeScript?

    Ans:

    In TypeScript, the import() syntax is used for dynamic imports, allowing you to import modules conditionally or lazily at runtime. This helps in reducing the initial bundle size of your application by loading modules only when they are needed. The import() syntax is used for dynamic imports, allowing you to load modules asynchronously and lazily at runtime. It returns a Promise for the imported module.

    72. What is the const syntax used for in TypeScript?

    Ans:

    In TypeScript, the as const syntax is used to assert literal values to have a “const” or “literal” type. When applied to an object or array, it ensures that every property or element is treated as a literal value rather than a variable, as const is used to infer literal types for objects, ensuring that object properties are treated as read-only constants rather than mutable variables.

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    73. How can you use TypeScript with Express.js for server-side development?

    Ans:

    • Install Dependencies: npm install -g typescript npm install express @types/express ts-node.
    • Create tsconfig.json: Configure TypeScript with a tsconfig.json file.
    • Project Structure: Organize with a src folder and entry file (e.g., app.ts).
    • Write TypeScript Code: Use TypeScript syntax in src for Express.js app.
    • Run with ts-node: Execute with ts-node (e.g., ts-node src/app.ts).

    74. How does TypeScript support tuple types?

    Ans:

    • In TypeScript, tuple types allow you to express an array where the type of a fixed number of elements is known, and the order of those types is significant.
    • Can define a tuple type by specifying the types of its elements in a specific order within square brackets.
    • TypeScript supports tuple types to represent an array with a fixed number of elements, each of which may have a different type. For example:
    • let myTuple: [string, number] = [‘hello’, 42];.

    75. Explain the purpose of the –jsxFactory compiler option in TypeScript.

    Ans:

    The –jsxFactory compiler option in TypeScript specifies the function to use for creating JSX elements. By default, TypeScript assumes that the React library provides a global function called React.createElement for this purpose.–jsxFactory allows you to specify a custom factory function for JSX elements, providing flexibility in integrating TypeScript with different JSX frameworks.

    76. Explain the concept of ambient external modules in TypeScript.

    Ans:

    Ambient declarations allow you to define types of code that exist outside the TypeScript environment, often used for libraries written in JavaScript. External modules (now commonly referred to as “namespaces” or “modules”, depending on the TypeScript version) help organize and encapsulate code. Ambient external modules declare the structure of an external module without providing an actual implementation. They are useful for describing existing JavaScript modules.

    77. How can you use TypeScript with Babel for transpiration?

    Ans:

    • Install packages: npm install –save-dev @babel/core @babel/preset-env @babel/preset-typescript Create babel.config.js with presets.
    • Install TypeScript: npm install –save-dev typescript.
    • Generate tsconfig.json with npx tsc –init.
    • Adjust tsconfig.json if needed.
    • Modify package.json scripts: “build”: “babel src -d dist”.
    • Run the build script: npm run build.

    78. What is the purpose of the –strictBindCallApply compiler option in TypeScript?

    Ans:

    •  –strictBindCallApply enables stricter checking for bind, call, and apply methods, ensuring that the provided arguments match the function’s parameters.
    • There is no specific TypeScript compiler option named –strictBindCallApply.
    • New compiler options may have been introduced since then. Please refer to the official TypeScript documentation or release notes for the most up-to-date information on compiler options.
    • If this is a recent addition, I might need to be made aware of it.

    79. What are intersection types in TypeScript, and how do they work?

    Ans:

    In TypeScript, intersection types are used to combine multiple types into a single type that has all the features of each type. You represent an intersection type using the & operator. Intersection types combine multiple types into a single type that has all the properties of each constituent type. For example type Combined = TypeA & TypeB;

    80. How does TypeScript handle type narrowing with the in-operator?

    Ans:

    In TypeScript, the in operator is used for type narrowing in conditional statements. It checks if a property exists in an object, narrowing down the type accordingly. The in operator is used for type narrowing in TypeScript, allowing you to check if a property exists in an object, thus narrowing down the type.

    81. Explain the concept of conditional module loading using the import() syntax in TypeScript.

    Ans:

    The import() syntax in TypeScript allows for dynamically loading modules based on conditions, providing a way to import and use modules at runtime conditionally. When you use the import() syntax, TypeScript treats it as a dynamic import, and the imported module is fetched only when the code is executed, not during the initial module loading. This is particularly useful when you want to load modules conditionally based on runtime conditions.

    82. How does TypeScript handle type assertions with the keyword and angle brackets?

    Ans:

    Both keyword and angle brackets (< >) can be used for type assertions in TypeScript. They tell the compiler to treat a value as a different, more specific type.TypeScript allows type assertions using both the keyword and angle brackets (< >). The syntax is generally recommended for type assertions in TypeScript, as it is more readable and less prone to confusion. 

    83. What is the purpose of the declare keyword in TypeScript?

    Ans:

    • The declare keyword is used to tell TypeScript that the specified entity (variable, function, or module) exists, even though it might not be defined in the current TypeScript code.
    • In TypeScript, the declare keyword is used to tell the compiler that a variable, function, class, or module already exists and has been declared elsewhere.
    • It’s often used when working with external libraries or when you want to define types for variables that are not part of your TypeScript code but are available at runtime.

    84. How does TypeScript handle type aliasing and intersection types together?

    Ans:

    • In TypeScript, type aliasing and intersection types can be used together to create more complex and flexible type definitions.
    • Type aliasing allows you to create a name for any type, while intersection types combine multiple types into a single type.
    • TypeScript allows the combination of type aliasing and intersection types, enabling the creation of complex types that combine the properties of multiple types.

    85. How can you use conditional rendering in React components with TypeScript?

    Ans:

    In React components with TypeScript, you can use conditional rendering by employing conditional statements or ternary operators based on certain conditions. Conditional rendering in React components with TypeScript can be achieved by using ternary operators, logical && operators, or conditional statements, along with proper type checking.

    86. What are type guards, and how do they help improve type safety in TypeScript?

    Ans:

    In TypeScript, type guards are a way to narrow down the type of a variable within a certain block of code. They help improve type safety by providing more precise information about the types of variables at runtime. Type guards are functions or expressions that narrow down the type of a variable within a certain block of code. They are used to improve type safety and enable more precise type checking.

    87. Explain the use of the –esModuleInterop compiler option in TypeScript.

    Ans:

    The –esModuleInterop compiler option in TypeScript is used to simplify interoperability between CommonJS and ES modules. When enabled, TypeScript allows for easier use of default imports from CommonJS modules in ES module code. It helps when working with code that was written using different module systems, making the integration smoother.–esModuleInterop simplifies interoperability between CommonJS and ES modules by allowing default imports from CommonJS modules to behave like default imports from ES modules.

    88. How can you enforce immutability in TypeScript using mapped types?

    Ans:

    Mapped types, along with read-only and ReadonlyArray, can be used to enforce immutability in TypeScript by creating read-only versions of object properties or arrays. In TypeScript, you can enforce immutability using mapped types by creating a mapped type that makes all properties of an object read-only.

    89. What is the purpose of the import * as an alias from the ‘module’ syntax in TypeScript?

    Ans:

    • In TypeScript, import * as an alias from the ‘module’ syntax is used to import an entire module and assign it to a variable (alias in this case).
    • This allows you to access the exported members of the module using the alias variable.
    • It’s useful when you want to import the entire module or when dealing with modules that have a lot of exports, providing a convenient way to reference them through a single alias.
    • The import * as an alias from the ‘module’ syntax is used to import an entire module under a specific alias, allowing you to access its exports through the alias.

    90. How can you create and use global variables in TypeScript?

    Ans:

    Global variables in TypeScript can be declared using the declare keyword or by attaching them to the window object when working in a browser environment. In TypeScript, you can create and use global variables by declaring them outside of any function or block. Use the declare keyword to inform TypeScript that the variable already exists.

    91. Explain the role of the –strictPropertyInitialization compiler option in TypeScript.

    Ans:

    •  –strictPropertyInitialization ensures that class properties are definitely assigned in the constructor or initialized elsewhere, reducing the risk of potential runtime errors.
    • The –strictPropertyInitialization compiler option in TypeScript enforces stricter rules regarding property initialization.
    • When enabled, TypeScript ensures that all class properties are initialized in the constructor or through definite assignment assertions before they are accessed.
    • This helps catch potential runtime errors related to uninitialized properties, promoting safer and more robust code.

    92. How does TypeScript handle type checking for default values in function parameters?

    Ans:

    TypeScript performs type-checking on default values in function parameters based on the specified types. If the provided default value doesn’t match the expected type, a type error is reported.TypeScript uses the specified default values in function parameters to infer and assign types. When a default value is provided, TypeScript considers the type of that default value as the type for the parameter.

    93. What is the Readonly<T> utility type in TypeScript, and how can it be used?

    Ans:

    In TypeScript, the Readonly<T> utility type is used to create an immutable (read-only) version of a given type T. It ensures that once an object is created with this type, it’s properties cannot be modifiedReadonly<T> is a utility type in TypeScript that creates a new type with all properties of T set to read-only. It is commonly used to enforce immutability for object types.

    94. Explain the purpose of the key of type of construct in TypeScript.

    Ans:

    In TypeScript, the key type construct is used to obtain a union type of all keys from a given type. Type is used to reference the type of an object, and the key extracts the keys of that type. The key of type is used to obtain the keys to an object’s properties. When applied to the type of a module or class, it provides the keys of its properties as string literals.

    95. What are the benefits of using the strict compiler flag in TypeScript?

    Ans:

    • The strict compiler flag in TypeScript enables a set of strict type-checking options, 
    • Including noImplicitAny, 
    • StrictNullChecks, 
    • Leading to safer
    • More reliable code.

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