firebase pagination

pagination.js

//Javascript version
var Pagination = (function () {
    function Pagination(dataRef, perPage, order) {
        this.hasRecords = true;
        this._pageRecordCount = 0;
        this._cursor = "";
        this.dataRef = dataRef;
        this.perPage = perPage || 10;
        this.order = order || 'dsc';
    }
    Pagination.prototype._handleData = function (data) {
        var currentRecords = [];
        this.hasRecords = false;
        this._pageRecordCount = 0;
        this._cursor = "";
        if (data) {
            var entities = data;
            var entityKeys = Object.keys(entities);
            if (entityKeys.length > this.perPage) {
                (this.order == 'asc') ? (this._cursor = entityKeys.pop()) : (this._cursor = entityKeys.shift());
                this.hasRecords = true;
            }
            for (var _i = 0, entityKeys_1 = entityKeys; _i < entityKeys_1.length; _i++) {
                var entity = entityKeys_1[_i];
                this._pageRecordCount++;
                if (this._pageRecordCount <= this.perPage) {
                    var tempData = entities[entity];
                    tempData["id"] = entity;
                    (this.order == 'asc') ? (currentRecords.push(tempData)) : (currentRecords.unshift(tempData));
                }
            }
        }
        return new Promise(function (resolve, reject) {
            resolve(currentRecords);
        });
    };
    Pagination.prototype.fetchRecords = function () {
        var _this = this;
        var databaseRef = firebase.database().ref(this.dataRef);
        var orderByRef = databaseRef.orderByKey();
        var filterRef;
        var cursorRef;
        if (this._cursor) {
            cursorRef = (this.order == 'asc') ? orderByRef.startAt(this._cursor) : orderByRef.endAt(this._cursor);
        }
        else {
            cursorRef = orderByRef;
        }
        if (this.order == 'asc') {
            filterRef = cursorRef.limitToFirst(this.perPage + 1);
        }
        else {
            filterRef = cursorRef.limitToLast(this.perPage + 1);
        }
        return filterRef.once("value").then(function (data) {
            return _this._handleData(data.val());
        });
    };
    return Pagination;
}());