ng-class2

<!DOCTYPE html>
<html lang="en" ng-app>
    <head>
        <meta charset="utf-8">
        <title>ng-class2 </title>
        <style>
            .red{background-color:#001122;}
            .green{background-color:gray;}
            #box{
                width: 200px;
                height: 200px;
                transition:background-color 1s ease;
            }
        </style>
    </head>
    <body>
        <select ng-model="style" id="">
            <option value="red">红色</option>      
            <option value="green">绿色</option>      
        </select>
        <!-- <div id="box" ng-class="style"></div> -->
        <div id="box" ng-class="{red:style=='red',green:style=='green'}"></div>
        <script src="bower_components/angular/angular.js"></script>

    </body>
</html>