`this.types.append(` заменить на `this.types.push(`
String JS_DRAG_AND_DROP =
"var src=arguments[0],tgt=arguments[1];var dataTransfer={dropEff" +
"ect:'',effectAllowed:'all',files:[],items:{},types:[],setData:f" +
"unction(format,data){this.items[format]=data;this.types.push(" +
"format);},getData:function(format){return this.items[format];}," +
"clearData:function(format){}};var emit=function(event,target){v" +
"ar evt=document.createEvent('Event');evt.initEvent(event,true,f" +
"alse);evt.dataTransfer=dataTransfer;target.dispatchEvent(evt);}" +
";emit('dragstart',src);emit('dragenter',tgt);emit('dragover',tg" +
"t);emit('drop',tgt);emit('dragend',src);";
.......
executeJavaScript(JS_DRAG_AND_DROP, elem_drag, elem_drop);
.......