问在AngularJS中，如何在输入字段中输入有效数据时，在输入字段前显示绿色的刻度标记？

EN

<md-input-container class="md-block" flex> 
    <label>Current Password</label> 
    <md-icon md-svg-src="/images/icons/ic_lock_black_24px.svg"></md-icon>
    <input type="password" ng-model="changePassword.currentPassword" required name="curPass" minlength="6">
    <div ng-messages="chnagePasswordForm.curPass.$error">
        <div ng-message="required">Please enter valid password</div>
        <div ng-message="minlength">Password should be of eight or more characters</div>
    </div>
    <md-button ng-disabled="chnagePasswordForm.$invalid" class="md-raised md-primary enrolBtn" ng-click="changePassword()">Save</md-button>
</md-input-container>