Edit in JSFiddle

<div ng-app>
    <p ng-class="[style1, style2, style3]">Using Array Syntax</p>
    <input ng-model="style1" placeholder="請輸入 strkie or bold or red"><br />
    <input ng-model="style2" placeholder="請輸入 strkie or bold or red"><br />
    <input ng-model="style3" placeholder="請輸入 strkie or bold or red"><br />    
</div>    

.strike {
    text-decoration: line-through;
}
.bold {
    font-weight: bold;
}
.red {
    color: red;
}