Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

// Type alias for an object shape
type Point = {
    x: number;
    y: number;
};

// Type alias for a union — interfaces cannot do this
type Result<T> =
    | { success: true; data: T }
    | { success: false; error: string };

function divide(a: number, b: number): Result<number> {
    if (b === 0) return { success: false, error: "Division by zero" };
    return { success: true, data: a / b };
}

const r = divide(10, 2);
if (r.success) console.log(r.data); // 5

// Type alias for a primitive (useful for documentation)
type UserID = number;
type Email  = string;

// Type alias for a tuple
type Pair<A, B> = [A, B];
const entry: Pair<string, number> = ["score", 98];

// Interface extension vs type intersection
interface Base { id: number }
interface Extended extends Base { name: string } // interface

type BaseType     = { id: number };
type ExtendedType = BaseType & { name: string };  // type alias

// Both work the same for object shapes
const a: Extended     = { id: 1, name: "A" };
const b: ExtendedType = { id: 2, name: "B" };

// Only type aliases can express mapped types
type Optional<T> = { [K in keyof T]?: T[K] };
type PartialPoint = Optional<Point>; // { x?: number; y?: number }