JavaScript

CHALLENGE const output = []; output.push(typeof foo); try { output.push(typeof bar); } catch (e) { output.push(e.message); } var foo = () => 'foo'; let bar = () => 'bar'; console.log(output.join(' | '));

CHALLENGE const arr = [1, [2, 3], [4, [5, 6]]]; const a = arr.flat(); const b = arr.flat(Infinity); const c = arr.flatMap(x => Array.isArray(x) ? x : [x, x]); console.log(a, b, c);

CHALLENGE function* inner() { const x = yield 1; yield x + 1; return 100; } function* outer() { const result = yield* inner(); yield result; } const g = outer(); console.log(g.next().value, g.next(10).value, g.next().value, g.next().value);

CHALLENGE const obj = { value: 42, getValue: function() { return this.value; } }; const unboundGetValue = obj.getValue; const boundGetValue = unboundGetValue.bind(obj); const boundTwice = boundGetValue.bind({ value: 100 }); console.log( boundGetValue(), boundTwice(), unboundGetValue.call({ value: 7 }), obj.getValue.apply({ value: 99 }) );

CHALLENGE class EventBus { #listeners = new Map(); on(event, cb) { if (!this.#listeners.has(event)) this.#listeners.set(event, []); this.#listeners.get(event).push(cb); return this; } emit(event, ...args) { const cbs = this.#listeners.get(event) || []; return cbs.map(cb => cb(...args)); } } const bus = new EventBus(); bus.on('data', x => x * 2).on('data', x => x + 1); const results = bus.emit('data', 5); console.log(results, bus.emit('missing', 1));

CHALLENGE const x = 0; const y = ''; const z = null; const r1 = x ?? y ? 'A' : 'B'; const r2 = z ?? y ? 'C' : 'D'; console.log(r1, r2);

CHALLENGE async function run() { const results = await Promise.allSettled([ Promise.resolve(1), Promise.reject('error'), new Promise(resolve => setTimeout(() => resolve(3), 0)), ]); console.log(results.map(r => r.value ?? r.reason).join(',')); } run();

CHALLENGE class Counter { #count = 0; get value() { return this.#count; } set value(v) { if (v < this.#count) throw new RangeError('Cannot decrease'); this.#count = v; } } const c = new Counter(); c.value = 5; let msg; try { c.value = 3; } catch (e) { msg = e.message; } c.value = 10; console.log(msg, c.value);

CHALLENGE const obj = { b: 1, 2: 'two', a: 3, 1: 'one' }; console.log(Object.keys(obj).join(','), Object.values(obj).join(','));

CHALLENGE class Counter { static #total = 0; #id; constructor() { Counter.#total++; this.#id = Counter.#total; } get id() { return this.#id; } static get total() { return Counter.#total; } } class Special extends Counter { #label; constructor(label) { super(); this.#label = label; } get label() { return `${this.#label}-${this.id}`; } } const c1 = new Counter(); const c2 = new Special('x'); const c3 = new Special('y'); console.log(c1.id, c2.id, c3.label, Counter.total);

CHALLENGE const source = { count: 0, get value() { this.count++; return this.count; } }; const { value, ...rest } = source; const spread = { ...source }; console.log(value, spread.value, source.count, JSON.stringify(rest));