Алгоритм Пагинации

function paginate({current, max}) {
	if (!current || !max) return null

	let prev = current === 1 ? null : current - 1,
			next = current === max ? null : current + 1,
			items = [1]

	if (current === 1 && max === 1) return {current, prev, next, items}
	if (current > 4) items.push('…')

	let r = 2, r1 = current - r, r2 = current + r

	for (let i = r1 > 2 ? r1 : 2; i <= Math.min(max, r2); i++) items.push(i)

	if (r2 + 1 < max) items.push('…')
	if (r2 < max) items.push(max)

	return {current, prev, next, items}
}

for (let max = 1; max < 10; max+=2) {
	console.log(`max: ${max}`)
	for (let current = 1; current <= max; current++) {
		let pagination = paginate({current, max})
		console.log(`  c:${current}`, pagination.items)
	}
}

/*
Output:
max: 1
	c:1 [1]
max: 3
	c:1 [1, 2, 3]
	c:2 [1, 2, 3]
	c:3 [1, 2, 3]
max: 5
	c:1 [1, 2, 3, '…', 5]
	c:2 [1, 2, 3, 4, 5]
	c:3 [1, 2, 3, 4, 5]
	c:4 [1, 2, 3, 4, 5]
	c:5 [1, '…', 3, 4, 5]
max: 7
	c:1 [1, 2, 3, '…', 7]
	c:2 [1, 2, 3, 4, '…', 7]
	c:3 [1, 2, 3, 4, 5, '…', 7]
	c:4 [1, 2, 3, 4, 5, 6, 7]
	c:5 [1, '…', 3, 4, 5, 6, 7]
	c:6 [1, '…', 4, 5, 6, 7]
	c:7 [1, '…', 5, 6, 7]
max: 9
	c:1 [1, 2, 3, '…', 9]
	c:2 [1, 2, 3, 4, '…', 9]
	c:3 [1, 2, 3, 4, 5, '…', 9]
	c:4 [1, 2, 3, 4, 5, 6, '…', 9]
	c:5 [1, '…', 3, 4, 5, 6, 7, '…', 9]
	c:6 [1, '…', 4, 5, 6, 7, 8, 9]
	c:7 [1, '…', 5, 6, 7, 8, 9]
	c:8 [1, '…', 6, 7, 8, 9]
	c:9 [1, '…', 7, 8, 9]
*/

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