Edit in JSFiddle

<div ng-app>    
    <p ng-class="[style4, {orange: warning}]">Using Array and Map Syntax</p>
    <input ng-model="style4" placeholder="Type: bold, strike" aria-label="Type: bold, strike"><br>
    <label><input type="checkbox" ng-model="warning"> warning (apply "orange" class)</label>
</div>           

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