src/heappushpop.js

import {siftdown} from './core/index.js';

export default function heappushpop(heap, item) {
	const x = heap.data;
	const n = x.length;

	if (n === 0) return item;

	const compare = heap.compare;

	if (compare(item, x[0]) <= 0) return item;

	const smallest = x[0];

	x[0] = item;

	// Sift down the new root

	siftdown(compare, x, 0, n, 0);

	return smallest;
}