效果：

const menu = {
  state: {
    products: {},
    GLOBAL_CONFIG:GLOBAL_CONFIG['GLOBAL_CONFIG']
  },
  mutations: {
    get_product: function (state, products) {
        //商品列表
        state.products = products;
        for(let i = 0; i < state.products.length; i++){
            if(state.products[i]['image'
 
] != null){
                // state.products[i]['image'] = state.GLOBAL_CONFIG['base64Header'] + state.products[i]['image'];
                //下載圖片到本地
                this.commit('imgCache',state.products[i]);
            }else{
                //新增預設圖片
                state.products[i]['image'] = require
 
("../assets/file.png");
            }
        }
    },
    imgCache: function (state,imgObj) {
        mui.plusReady(function(){
            // 1. 轉換網路圖片地址為本地快取圖片路徑，判斷該圖片是否存在本地快取
            // http://...jpg -> md5
            // 快取目錄 _downloads/image/(md5).jpg
            let image_url           = imgObj.image;
            let
 
 image_md5           = md5(image_url);
            // 快取本地圖片url
            let local_image_url     = '_downloads/image/'+image_md5+'.jpg';
            // 平臺絕對路徑
            let absolute_image_path = plus.io.convertLocalFileSystemURL(local_image_url);
            console.log(absolute_image_path);
            // 判斷本地是否存在該檔案，存在就就直接使用，否則就下載
            plus.io.resolveLocalFileSystemURL( absolute_image_path, function( entry ) {
                if(entry){
                    imgObj.image = plus.io.convertLocalFileSystemURL(local_image_url);
                }else{
                    download_img();
                }
            }, function ( e ) {
                console.log("Resolve file URL failed: ");
                download_img();
            } );
            function download_img(){
                // filename:下載任務在本地儲存的檔案路徑
                let download_task = plus.downloader.createDownload(image_url, {
                    filename: local_image_url
                }, function(download, status) {
                    // 下載失敗,刪除本地臨時檔案
                    if(status != 200){
                        console.log('下載失敗,status'+status);
                        if(local_image_url != null){
                            plus.io.resolveLocalFileSystemURL(local_image_url, function(entry) {
                                entry.remove(function(entry) {
                                    console.log("臨時檔案刪除成功" + local_image_url);
                                    // 重新下載圖片
                                    download_img();
                                }, function(e) {
                                    console.log("臨時檔案刪除失敗" + local_image_url);
                                });
                            });
                        }
                    }else{
                        // 把下載成功的圖片顯示
                        // 將本地URL路徑轉換成平臺絕對路徑
                        console.log("下載成功" + local_image_url);
                        imgObj.image = plus.io.convertLocalFileSystemURL(local_image_url);
                    }
                });
                download_task.start();
            }       
        });
    }
  },
  actions: {

  }
}