Basic Data Types
TypeScript provides type annotations to explicitly define primitive data types and special safety types.
1. Primitive Types
| Type | Description | Code Example |
|---|---|---|
number | Integers, floats, hexadecimal, binary values | let count: number = 42; |
string | Textual data, template literals | let name: string = "Alice"; |
boolean | True or false values | let isActive: boolean = true; |
2. Type Inference
You don't always have to write explicit types! TypeScript automatically infers the variable type based on its initial value:
// TypeScript automatically infers message as string let message = "Hello World"; // ❌ Error: Type 'number' is not assignable to type 'string' message = 123;
3. `any` vs `unknown` (Type Safety Comparison)
Both any and unknown accept any value, but unknown is type-safe because it forces you to perform type checking before performing operations!
`any` (Disables Type Checking):
let data: any = "Hello"; data.toUpperCase(); // OK data(); // 💥 Crashes at runtime!
`unknown` (Type-Safe Escape Hatch):
let data: unknown = "Hello";
// ❌ Error: Property 'toUpperCase' does not exist on type 'unknown'
// data.toUpperCase();
if (typeof data === "string") {
console.log(data.toUpperCase()); // Safe!
}4. `void` vs `never`
// void: Function returns nothing (undefined)
function logMessage(msg: string): void {
console.log(msg);
}
// never: Function NEVER returns (throws error or infinite loop)
function throwError(errorMsg: string): never {
throw new Error(errorMsg);
}Next Up
Learn typed arrays, fixed-length tuples, and readonly arrays in TypeScript.
Next Lesson: Arrays & Tuples →
