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// sample.ts
// A practical TypeScript tour in one file 🚀
// --------------------
// Basic Types
// --------------------
let username: string = "Alice";
let age: number = 30;
let isAdmin: boolean = false;
let hobbies: string[] = ["gaming", "coding"];
let scores: Array<number> = [10, 20, 30];
// Tuple
let userTuple: [string, number] = ["Bob", 42];
// --------------------
// Enums
// --------------------
enum Role {
User = "USER",
Admin = "ADMIN",
Moderator = "MODERATOR",
}
// --------------------
// Interfaces & Types
// --------------------
interface User {
id: number;
name: string;
role: Role;
email?: string; // optional
}
type ApiResponse<T> = {
success: boolean;
data: T;
error?: string;
};
// --------------------
// Functions
// --------------------
function greet(user: User): string {
return `Hello, ${user.name}! Your role is ${user.role}.`;
}
const add = (a: number, b: number): number => a + b;
// Function with default value
function log(message: string, level: "info" | "warn" | "error" = "info") {
console.log(`[${level.toUpperCase()}] ${message}`);
}
// --------------------
// Classes
// --------------------
class UserService {
private users: User[] = [];
constructor(initialUsers: User[] = []) {
this.users = initialUsers;
}
addUser(user: User): void {
this.users.push(user);
}
findByRole(role: Role): User[] {
return this.users.filter(u => u.role === role);
}
}
// --------------------
// Generics
// --------------------
function wrapResponse<T>(data: T): ApiResponse<T> {
return {
success: true,
data,
};
}
// --------------------
// Async / Await
// --------------------
async function fetchUser(id: number): Promise<User> {
// Fake async call
return new Promise(resolve => {
setTimeout(() => {
resolve({
id,
name: "Charlie",
role: Role.User,
});
}, 500);
});
}
// --------------------
// Type Narrowing
// --------------------
function printValue(value: string | number) {
if (typeof value === "string") {
console.log("String value:", value.toUpperCase());
} else {
console.log("Number value:", value.toFixed(2));
}
}
// --------------------
// Usage Example
// --------------------
(async () => {
const user: User = {
id: 1,
name: username,
role: isAdmin ? Role.Admin : Role.User,
};
log(greet(user));
const service = new UserService([user]);
service.addUser({ id: 2, name: "Dana", role: Role.Admin });
console.log("Admins:", service.findByRole(Role.Admin));
const fetchedUser = await fetchUser(3);
const response = wrapResponse(fetchedUser);
console.log("API response:", response);
printValue("hello");
printValue(123.456);
console.log("2 + 3 =", add(2, 3));
})();
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