Nodejs simple pagination

help.js

const help = {
    genPagination: (pageLength, fullPageSelectedIndex) => {
        const fullPage = Array.from(Array(pageLength)).map((v, i) => i)
        if (fullPage.length < 11) return fullPage

        let minLeftCut = 2
        let maxLeftCut = 6

        let minRightCut = 2
        let maxRightCut = 6

        let leftPrefix = 2
        let minLeftPrefix = 6

        let rightPrefix = 2
        let minRightPrefix = 6

        let leftSide = fullPage.slice(0, fullPageSelectedIndex)
        let rightSide = fullPage.slice(fullPageSelectedIndex + 1)
        let selectedValue = fullPage[fullPageSelectedIndex]

        if (leftSide.length >= minLeftPrefix) {
            let leftCut = maxLeftCut - rightSide.length < minLeftCut ? minLeftCut : maxLeftCut - rightSide.length
            leftSide = fullPage.slice(0, leftPrefix).concat(['...']).concat(leftSide.slice(-leftCut))
        }

        if (rightSide.length >= minRightPrefix) {
            let rightCut = maxRightCut - leftSide.length < minRightCut ? minRightCut : maxRightCut - leftSide.length
            rightSide = rightSide.slice(0, rightCut).concat(['...']).concat(fullPage.slice(-rightPrefix))
        }

        return leftSide.concat(selectedValue).concat(rightSide)
    },
}

module.exports = help

// There are 420 pages in total
// The page 69 is currently selected
// Generate the pagination layout
const page = help.genPagination(420, 69)
// First page start at index 0
// page = [0, 1, "...", 67, 68, 69, 70, 71, "...", 418, 419]