bench_array_from.js
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bench_array_from.js
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	const ITERATIONS = 1_000_000;
	const source = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
	const mapFn = x => x * 2;

	// --- Polyfill ---
	const ArrayFrom_polyfill = function (src, mapFn, thisArg) {
	if (src == null) {
	console.error('TypeError: Cannot convert undefined or null to object');
	return [];
	}
	if (mapFn !== undefined && typeof mapFn !== 'function') {
	console.error('TypeError: mapFn is not a function');
	return [];
	}
	const arr = [];
	let i = 0;
	if (src[Symbol.iterator] != null) {
	for (const v of src) arr.push(mapFn ? mapFn.call(thisArg, v, i++) : v);
	} else {
	const len = src.length >>> 0;
	for (; i < len; i++) arr.push(mapFn ? mapFn.call(thisArg, src[i], i) : src[i]);
	}
	return arr;
	};

	// --- Builtin ---
	function benchBuiltin() {
	const start = performance.now();
	for (let i = 0; i < ITERATIONS; i++) {
	Array.from(source, mapFn);
	}
	return performance.now() - start;
	}

	// --- Polyfill ---
	function benchPolyfill() {
	const start = performance.now();
	for (let i = 0; i < ITERATIONS; i++) {
	ArrayFrom_polyfill(source, mapFn);
	}
	return performance.now() - start;
	}

	const builtinMs = benchBuiltin();
	const polyfillMs = benchPolyfill();

	console.log(`Array.from (builtin): ${builtinMs.toFixed(2)} ms`);
	console.log(`Array.from (polyfill): ${polyfillMs.toFixed(2)} ms`);
	console.log(`Ratio: builtin is ${(polyfillMs / builtinMs).toFixed(2)}x ${polyfillMs > builtinMs ? 'faster' : 'slower'} than polyfill`);