Generic pagination service for calculating paginate essentials

pagination.service.ts

/*
 * Export as a type
 */
export const paginationService = {
    getPager,
}
/*
 * Get pager related data
 */
function getPager(
    totalItems: number,
    currentPage: number = 1,
    pageSize: number = 10
) {
    // calculate total pages
    let totalPages = Math.ceil(totalItems / pageSize)

    // ensure current page isn't out of range
    if (currentPage < 1) {
        currentPage = 1
    } else if (currentPage > totalPages) {
        currentPage = totalPages
    }

    let startPage: number, endPage: number
    if (totalPages <= 10) {
        // less than 10 total pages so show all
        startPage = 1
        endPage = totalPages
    } else {
        // more than 10 total pages so calculate start and end pages
        if (currentPage <= 6) {
            startPage = 1
            endPage = 10
        } else if (currentPage + 4 >= totalPages) {
            startPage = totalPages - 9
            endPage = totalPages
        } else {
            startPage = currentPage - 5
            endPage = currentPage + 4
        }
    }

    // calculate start and end item indexes
    let startIndex = (currentPage - 1) * pageSize
    let endIndex = Math.min(startIndex + pageSize - 1, totalItems - 1)

    // create an array of pages to ng-repeat in the pager control
    let pages = Array.from(Array(endPage + 1 - startPage).keys()).map(
        (i) => startPage + i
    )

    // return object with all pager properties required by the view
    return {
        totalItems: totalItems,
        currentPage: currentPage,
        pageSize: pageSize,
        totalPages: totalPages,
        startPage: startPage,
        endPage: endPage,
        startIndex: startIndex,
        endIndex: endIndex,
        pages: pages,
    }
}