<body> <div id='root'></div> <script src="./react.js"></script> <script src="./react-dom.js"></script> <script src="./babel.min.js"></script> <script type="text/babel"> var arr=['111','222','333'] //只给第一项加active 如果多项要active 可以用插件,后面讲 ReactDOM.render(( <ul> {arr.map((val,index)=>{ return (<li key={index} className={index==0?'active':''}>{index}---{val}</li>) }) } </ul> ),document.getElementById('root')) </script>