TypeScript Data Types

1️⃣ What Are Data Types in TypeScript?

Data types define what kind of value a variable can store. In TypeScript, variables must have a type to prevent errors.

Example:

let name: string = "Alice";  // Only a string can be assigned
let age: number = 25; // Only a number can be assigned
let isActive: boolean = true; // Only true or false can be assigned

🚀 Why use data types?
✔ Prevents errors before running the program
✔ Makes code more readable
✔ Improves performance by detecting mistakes early

2️⃣ Built-in Data Types in TypeScript

TypeScript provides the following basic data types:

Data TypeExampleDescription
string“Hello”Stores text values
number25, 3.14Stores integer and floating-point numbers
booleantrue, falseStores true or false values
anyanythingCan store any type of value (not recommended)
unknownanythingSimilar to any but safer
voidundefinedUsed for functions that do not return a value
neverneverRepresents values that never occur
array[1, 2, 3]Stores a collection of values
tuple[1, “Hello”]A fixed-length array with different types
enumenum Color {Red, Green, Blue}Stores a set of named constants
object{ key: “value” }Stores complex data structures

Let’s understand each type with examples.

3️⃣ string Data Type (Text Values)

The string type is used for text values. You must enclose strings in single ( ‘ ) or double ( ” ) quotes.

Example:

let firstName: string = "John";
let message: string = "Welcome to TypeScript!";
console.log(firstName, message);

✔ Using template literals (backticks ` `):

let user: string = "Alice";
let greeting: string = `Hello, ${user}!`; // ✅ Works with variables
console.log(greeting);

Best Practice: Always use string for text values instead of any.

4️⃣ number Data Type (Numbers & Decimals)

The number type stores both integers and floating-point numbers.

Example:

let age: number = 25;
let price: number = 99.99;
let hex: number = 0xff; // Hexadecimal
let binary: number = 0b1010; // Binary
let octal: number = 0o123; // Octal
console.log(age, price, hex, binary, octal);

Best Practice: Use number instead of any for calculations.

5️⃣ boolean Data Type (True or False)

The boolean type stores true or false values.

Example:

let isLoggedIn: boolean = true;
let hasPermission: boolean = false;
console.log(isLoggedIn, hasPermission);

🚀 Why use boolean?
✔ Makes code more readable and logical
✔ Prevents mistakes when checking conditions

6️⃣ any Data Type (Avoid Using It!)

The any type allows a variable to hold any kind of value. It removes type safety, so avoid using it.

Example:

let data: any = 42;
data = "Hello"; // ✅ Allowed, but not recommended
data = true;
console.log(data);

🚫 Why avoid any?
✔ No type checking – Errors can go unnoticed
✔ Code becomes unpredictable

Best Practice: Use specific types instead of any.

7️⃣ unknown Data Type (Safer than any)

The unknown type is like any, but it forces type checking before usage.

Example:

let value: unknown;
value = 42;
value = "Hello";
// value.toUpperCase(); // ❌ Error: Must check type first

if (typeof value === "string") {
console.log(value.toUpperCase()); // ✅ Works
}

Best Practice: Prefer unknown over any when you don’t know the exact type.

8️⃣ void Data Type (For Functions Without Return Values)

The void type is used when a function does not return anything.

Example:

function logMessage(): void {
console.log("This function returns nothing!");
}

Best Practice: Use void for functions that only perform actions (like logging data).

9️⃣ never Data Type (For Impossible Values)

The never type is used for functions that never return a value (like errors or infinite loops).

Example:

function throwError(message: string): never {
throw new Error(message);
}

Best Practice: Use never for functions that always throw errors.

🔟 array Data Type (Lists of Values)

Arrays store multiple values of the same type.

Example:

let numbers: number[] = [1, 2, 3, 4, 5];
let names: string[] = ["Alice", "Bob", "Charlie"];
console.log(numbers, names);

✔ Using Array<T> syntax:

let scores: Array<number> = [100, 90, 80];
console.log(scores);

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