TypeScript Types

Introduction

In this chapter, we will explore the various types available in TypeScript. Types in TypeScript are used to describe the shape and behavior of data. They enable TypeScript to perform static type checking, helping you catch errors early in the development process.

Table of Contents

1. Basic Types
2. • Number
   • String
   • Boolean
   • Any
   • Void
   • Null and Undefined
   • Never
   • Unknown
3. Array Types
4. Tuple Types
5. Enum Types
6. Conclusion

Basic Types

Number

The number type represents numeric values, including both integers and floating-point numbers.

Syntax

let variableName: number = value;

Example

Here, we declare a variable age using number and assign it a value of 25, and another variable pi with a floating-point value.

let age: number = 25;
let pi: number = 3.14;
console.log(age, pi); // Output: 25 3.14

String

The string type represents textual data.

Syntax

let variableName: string = value;

Example

Here, we declare a variable name using string and assign it a value, and another variable greeting that uses template literals.

let name: string = "Ravi";
let greeting: string = `Hello, ${name}!`;
console.log(name, greeting); // Output: Ravi Hello, Ravi!

Boolean

The boolean type represents true or false values.

Syntax

let variableName: boolean = value;

Example

Here, we declare two variables isStudent and hasGraduated using boolean and assign them true and false values, respectively.

let isStudent: boolean = true;
let hasGraduated: boolean = false;
console.log(isStudent, hasGraduated); // Output: true false

Any

The any type allows a variable to hold any type of value. It is useful for scenarios where the type of a value is not known at compile-time.

Syntax

let variableName: any = value;

Example

Here, we declare a variable randomValue using any and assign it different types of values.

let randomValue: any = 42;
randomValue = "Hello";
randomValue = true;
console.log(randomValue); // Output: true

Void

The void type represents the absence of any value. It is commonly used as the return type of functions that do not return a value.

Syntax

function functionName(): void {
  // function body
}

Example

Here, we declare a function logMessage that takes a string parameter and logs it to the console. The function does not return any value.

function logMessage(message: string): void {
  console.log(message);
}
logMessage("Hello, TypeScript!"); // Output: Hello, TypeScript!

Null and Undefined

The null and undefined types represent the absence of a value and an uninitialized value, respectively.

Syntax

let variableName: null = null;
let variableName: undefined = undefined;

Example

Here, we declare variables emptyValue and uninitializedValue using null and undefined types, respectively.

let emptyValue: null = null;
let uninitializedValue: undefined = undefined;
console.log(emptyValue, uninitializedValue); // Output: null undefined

Never

The never type represents values that never occur, such as the return type of a function that always throws an error or never returns.

Syntax

function functionName(): never {
  // function body
}

Example

Here, we declare a function error that throws an error and never returns.

function error(message: string): never {
  throw new Error(message);
}
// error("This is an error"); // Uncommenting this line will throw an error: Uncaught Error: This is an error

Unknown

The unknown type represents a value that could be any type. It is safer than any because it forces the developer to perform type checking before using the value.

Syntax

let variableName: unknown = value;

Example

Here, we declare a variable value using unknown and then perform type checking before using it.

let value: unknown = "Hello, World!";
if (typeof value === "string") {
  console.log(value.toUpperCase()); // Output: HELLO, WORLD!
}

Array Types

An array type represents a collection of values of the same type.

Syntax

let arrayName: type[] = [value1, value2, ...];

Example

Here, we declare an array numbers of number type and an array names of string type.

let numbers: number[] = [1, 2, 3, 4, 5];
let names: string[] = ["Ravi", "Ankit", "Priya"];
console.log(numbers, names); // Output: [1, 2, 3, 4, 5] ["Ravi", "Ankit", "Priya"]

Tuple Types

A tuple type represents an array with a fixed number of elements of specific types.

Syntax

let tupleName: [type1, type2, ...] = [value1, value2, ...];

Example

Here, we declare a tuple person with a string and a number type.

let person: [string, number] = ["Ravi", 25];
console.log(person); // Output: ["Ravi", 25]

Enum Types

An enum type is a way to define a set of named constants. It is useful for representing a collection of related values.

Syntax

enum EnumName {
  Constant1,
  Constant2,
  ...
}

Example

Here, we declare an enum Direction with four named constants and use it to set the value of move.

enum Direction {
  Up,
  Down,
  Left,
  Right
}

let move: Direction = Direction.Up;
console.log(move); // Output: 0

Conclusion

In this chapter, we covered the various types available in TypeScript, including basic types, array types, tuple types, and enum types. We provided examples to illustrate how these types work in TypeScript. Understanding these types is essential for writing robust and error-free TypeScript code. In the next chapter, we will delve deeper into TypeScript interfaces and how to use them effectively.