| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| module.exports = { |
| /** |
| * Divide source array in chunks, then push each chunk into destination array |
| * with delay time one by one. So then destination array gets more and more items |
| * till all items are loaded. |
| * @param options |
| * options.initSize - number of items which will be pushed in array immediately |
| * options.chunkSize - number of items which will be pushed after defined delay |
| * options.delay - interval between each chunk push |
| * options.destination - array where items will be pushed |
| * options.source - source of items |
| * options.context - the object that should know when data is completely loaded, |
| * lazy loading will define "isLoaded" property for context object and update it |
| * @return {Object} - instance of lazy loading run |
| */ |
| run: function (options) { |
| var initSize = options.initSize || 25, |
| chunkSize = options.chunkSize || 50, |
| delay = options.delay || 300, |
| destination = options.destination, |
| source = options.source, |
| self = this, |
| instance = { |
| context: options.context, |
| timeoutRef: null |
| }, |
| chunks; |
| if (Array.isArray(destination) && Array.isArray(source)) { |
| destination.pushObjects(source.slice(0, initSize)); |
| if(source.length > initSize) { |
| chunks = this.divideIntoChunks(source.slice(initSize, source.length), chunkSize); |
| this.pushChunk(chunks, 0, delay, destination, instance); |
| } else { |
| instance.context.set('isLoaded', true); |
| } |
| } |
| return instance; |
| }, |
| |
| /** |
| * push chunks into destination array in delay time |
| * @param chunks |
| * @param index |
| * @param delay |
| * @param destination |
| * @param instance |
| */ |
| pushChunk: function (chunks, index, delay, destination, instance) { |
| var self = this; |
| instance.timeoutRef = setTimeout(function () { |
| destination.pushObjects(chunks[index]); |
| if (chunks.length === (++index)) { |
| instance.context.set('isLoaded', true); |
| } else { |
| self.pushChunk(chunks, index, delay, destination, instance); |
| } |
| }, delay); |
| }, |
| |
| /** |
| * divide source array into chunks |
| * @param source |
| * @param chunkSize |
| * @return {Array} |
| */ |
| divideIntoChunks: function (source, chunkSize) { |
| var chunk = []; |
| var chunks = []; |
| var counter = 0; |
| source.forEach(function (item) { |
| counter++; |
| chunk.push(item); |
| if (counter === chunkSize) { |
| chunks.push(chunk); |
| chunk = []; |
| counter = 0; |
| } |
| }); |
| if (chunk.length > 0) { |
| chunks.push(chunk); |
| } |
| return chunks; |
| }, |
| /** |
| * terminate lazy loading run |
| * @param instance - lazy loading instance |
| */ |
| terminate: function (instance) { |
| clearTimeout(instance.timeoutRef); |
| } |
| }; |