TypeScript Interview Questions and Answers

1. Explain the data types available in TypeScript.

TypeScript provides the following data types:

Built-in Data Types

• string – Stores text values.
  number – Stores numeric values.
  boolean – Stores True or false.
  null – Represents an empty value.
  undefined – Represents an uninitialized variable.
  any – Accepts values of any type.
  unknown – Stores values of unknown type safely.
  void – Used for functions that do not return a value.
  never – Used for functions that never return.

User-defined Data Types

• Array – Stores multiple values of the same type.
  Tuple – Stores a fixed number of values with different data types.
  Enum – Defines a set of named constants.
  Class – Creates objects with properties and methods.
  Interface – Defines the structure of an object.
  Type Alias – Creates a custom name for an existing type.

2. In how many ways can we declare variables in TypeScript?

TypeScript provides three ways to declare variables:

• var – Function-scoped. It can be redeclared and updated. Generally not recommended in modern TypeScript.
• let – Block-scoped. It can be updated but cannot be redeclared within the same scope.
• const – Block-scoped. It cannot be reassigned after initialization.

Code Example

// var
var age = 25;
var age = 30; // Allowed (redeclared)
age = 35;     // Allowed (updated)

// let
let name = "Shiv";
name = "Sara"; // Allowed (updated)
// let name = "John"; // Error: Cannot redeclare block-scoped variable

// const
const country = "India";
// country = "USA"; // Error: Cannot reassign a const variable

// Display Output
document.write("
Output
");
document.write("age = " + age + "
");
document.write("name = " + name + "
");
document.write("country = " + country);