Data Types in TypeScript

Data types define the kind of data a variable can hold, ensuring better organization, fewer errors, and improved code readability. In TypeScript, strong typing is used to catch errors early, making your code more reliable and maintainable.

TypeScript supports a wide range of data types, from simple types like boolean, number, and string to more complex ones like arrays, tuples, and enums. By understanding and using these data types effectively, developers can write robust and predictable code.

1. Boolean

A boolean represents either true or false. It is used to control logic, such as deciding whether a condition is met or not.

Use Case:
Tracking on/off states like a toggle switch or user login status.

1let isActive: boolean = true;
2let hasCompleted: boolean = false;

2. Number

The number type represents all numeric values, including integers and floating-point numbers. It is used for calculations, counters, and numeric operations.

Use Case:
Storing quantities, ages, or mathematical results.

1let age: number = 25;
2let pi: number = 3.14;

3. String

A string stores textual data, like names or messages. It supports template literals for dynamic content.

Use Case:
Storing user names, messages, or content that needs to be displayed.

1let welcomeMessage: string = `Welcome, John!`;

4. Array

Arrays are used to store multiple values of the same type in an ordered collection.

Use Case:
Storing lists like product names, user IDs, or numerical data.

1let scores: number[] = [85, 90, 78];

5. Tuple

Tuples store a fixed number of elements with specified types, such as a combination of related values.

Use Case:
Storing grouped data, like a user’s name and age together.

1let userInfo: [string, number] = ["Alice", 25];

6. Enum

An enum defines a set of named constants, making code more readable and meaningful.

Use Case:
Representing predefined options like user roles or statuses.

1enum Role { Admin, User, Guest }
2let userRole: Role = Role.Admin;

7. Unknown

The unknown type is safer than any and requires type checking before use. It is useful for values with uncertain types.

Use Case:
Handling external input like user-provided data or API responses.

1let data: unknown = "Hello";
2if (typeof data === "string") {
3  console.log(data.toUpperCase());
4}

8. Any

The any type can hold any value and bypasses TypeScript’s type checking. It should be used sparingly.

Use Case:
Dealing with legacy code or highly dynamic data.

1let randomValue: any = 42;
2randomValue = "A string now!";

9. Void

The void type indicates a function doesn’t return a value. It’s used for functions that perform actions rather than calculations.

Use Case:
Logging messages or triggering events.

1function logMessage(msg: string): void {
2  console.log(msg);
3}

10. Null and Undefined

These types represent the absence of a value. null is used for explicitly empty values, while undefined means a variable hasn’t been initialized.

Use Case:
Handling optional fields or empty data.

1let result: null = null;
2let value: undefined = undefined;

11. Never

The never type is used for functions that never return, such as those that throw errors or run infinitely.

Use Case:
Error handling or indicating unreachable code.

1function throwError(msg: string): never {
2  throw new Error(msg);
3}

12. Object

The object type represents non-primitive values like arrays, functions, or plain objects.

Use Case:
Storing structured data like user profiles or settings.

1let user: object = { name: "John", age: 30 };

13. Type Assertions

Type assertions allow you to manually specify a type when TypeScript cannot infer it accurately.

Use Case:
When the developer knows more about a variable’s type than TypeScript.

1let value: any = "Hello";
2let valueLength: number = (value as string).length;