Pagination Helpers1. centeredRange - generates a centered range ([start, end]) based on a number and range length2. boundRange - safely and efficiently bounds a range while maintaining the range length if possible

Centered, Bounded Range

function centeredRange(number, length) {
    // Find starting number as about half of the range length to the left (favoring forward)
    number += 1 - Math.ceil(length / 2);
    // Find ending number as a length's distance away, minus 1 because the starting number counts towards the length
    return [number, number + length - 1];
}

function boundRange(range, min, max) {
    // If end > max, shift range backward by the difference
    var start = range[0] + Math.min(max - range[1], 0);
    var end = range[1] + Math.min(max - range[1], 0);

    // If start < min, shift range forward by the difference
    // Then, with shifts complete, crop the range
    return [
        Math.max(start + Math.max(min - start, 0), min),
        Math.min(end + Math.max(min - start, 0), max)
    ];
}