Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

// Primitives
const name: string = "Alice";
const age: number = 30;
const big: bigint = 9007199254740993n;
const active: boolean = true;
const sym: symbol = Symbol("id");
const nothing: null = null;
const missing: undefined = undefined;

// any — escape hatch, avoid when possible
let wild: any = "hello";
wild = 42;
wild.foo.bar; // no error — dangerous

// unknown — type-safe any
let input: unknown = getUserInput();
// input.toUpperCase(); // Error — must narrow first
if (typeof input === "string") {
    console.log(input.toUpperCase()); // OK after narrowing
}

// never — unreachable code / exhaustive checks
function fail(message: string): never {
    throw new Error(message);
}

function assertNever(x: never): never {
    throw new Error(`Unexpected value: ${x}`);
}

// void — no meaningful return value
function logMessage(msg: string): void {
    console.log(msg);
    // returning undefined is allowed, returning a value is not
}

// Tuple — fixed-length typed array
const pair: [string, number] = ["Alice", 30];
const [user, score] = pair;

function getUserInput(): unknown { return "hello"; }