Paginator Helper

paginator.js

// Paginator Helper Class
class PaginationHelper {

    constructor(collection, itemsPerPage) {
        this.collection = collection
        this.itemsPerPage = itemsPerPage
    }

    itemCount() {
        return this.collection.length
    }

    pageCount() {
        return Math.ceil(this.itemCount() / this.itemsPerPage)
    }

    pageItemCount(pageIndex) {
        if (isNaN(pageIndex) || pageIndex < 0 || pageIndex >= this.pageCount()) {
            return -1
        }
        if (pageIndex === this.pageCount() - 1) {
            const itemsOffset = pageIndex * this.itemsPerPage
            return this.itemCount() - itemsOffset
        }
        if (pageIndex < this.pageCount() - 1) {
            return this.itemsPerPage
        }
    }

    pageIndex(itemIndex) {
        if (isNaN(itemIndex) || itemIndex < 0 || itemIndex >= this.itemCount()) {
            return -1
        }
        return Math.floor(itemIndex / this.itemsPerPage)
    }
}