Angular -- ng-class

1.
<div ng-class {'selected': isSelected, 'car': isCar}">

    当 isSelected = true 则增加selected class，
    当isCar=true,则增加car class，

    2.

<div ng-class="{true: 'active', false: 'inactive'}[isActive]">
</div>

    isActive表达式为true，则 active，否则inactive。

    3.

    <div class=”{{test}}”></div>