var list=[];

for(var one of this.state.themeDataList){


 var b=(<List imageUrl={Util.serverAddr+'/image?id='+one['_id']} themeData={imageList} key={one['_id']}>
 </List>);
 list.push(b);

}

等同于
list=[...this.state.themeDataList].map(a=><List imageUrl={Util.serverAddr+'/image?id='+a['_id']} themeData={imageList} key={a['_id']}>
  </List>)