javascript 动态加载javascript文件

     /*
         loadFile(data, callback): 动态加载js文件
         data: 存放需要加载的js文件的url("url" || ["url", "url"])
         callback: 加载完成回调函数
     */
     function loadFile(data, callback){
         if(!data){return;}
         let k, arr = [], el = document.body;
         if(typeof(data) === 'string'){arr.push(data);}
         else if(Array.isArray(data) === true){for(k in data){arr.push(data[k]);}}
         else{return;}

         let load = (url, suc, err)=>{
             let script = document.createElement('script');
             script.type = "text/javascript";//type = 'module';
             script.src = url;
             el.appendChild(script);
             script.onload = function (e){if(typeof(suc) === "function"){suc(e);}}
             script.onerror = function (e){if(typeof(err) === "function"){err(e);}}
         }

         let timeout = ()=>{
             if(t === len){if(typeof(callback) === "function"){callback(t, len, arr);} return;}
             setTimeout(timeout, 1000);
         }

         let len = arr.length, t = 0;
         for(k in arr){load(arr[k], (e)=>{t++;});}
         timeout();
     }
     //调用
     loadFile("./main.js", (t, len, arr)=>{document.write(t+" "+len+" "+arr)});
     loadFile(["./main.js", "./init.js"], (t, len, arr)=>{document.write(t+" "+len+" "+arr)});