Konami code in 7 lines of RxJS

konami.ts

import {find, fromEvent, scan} from 'rxjs';

const up = "ArrowUp", down = "ArrowDown", left = "ArrowLeft", right = "ArrowRight";
const sequence = [up, up, down, down, left, right, left, right, "b", "a"];

fromEvent<KeyboardEvent>(document, 'keyup').pipe(
    scan((i, {key}) => (sequence[i] == key) ? i+1 : 0, 0),
    find(i => i == sequence.length)
).subscribe(() => console.log("unlocked"))