2.备选字符集

    <!-- 备选字符集 -->
    <script>
        var str = "上海，上天，上到那里去";
        var reg = /上[海天]/g; //上海或者上天
        // var reg = /[上海天]/g;//上或海或天
        console.log(str.replace(reg,"$"));
    </script>
    <script>
        var a = "hello world";
        var b = /l|e/g; //遇到l或者e
        console.log(a.replace(b,"$"));
    </script>