control.js

app.controller('HomeController', ['$scope', 'emails', function($scope, emails) {
  emails.success(function(data) {
    $scope.emails = data;
  });

//   $scope.emails = [
//         {
//         from: "Shawn Carter",
//         datetime: 1420816800000,
//         subject: "Current state of mind",
//         message: "Yeah I'm out that Brooklyn, now I'm down in Tribeca. Want to check out that new bistro?",
//         unread: true
//         },
//         {
//         from: "Jason Cornwell",
//         datetime: 1420809000000,
//         subject: "Please return my stapler",
//         message: "Hey my stapler is missing again. Please return it.",
//         unread: true
//         },
//         {
//         from: "Google Voice",
//         datetime: 1420694340000,
//         subject: "New voicemail from (877) 466-4411 at 5:19 AM",
//         message: "Missed call from: (877) 466-4411 at 9:05 AM",
//         unread: false
//         },
//         {
//         from: "Antwan Patton",
//         datetime: 1420543620000,
//         subject: "Shutterbugg",
//         message: "Hey man, did you have a chance to check out the new app? Just released it for iOS and Android. Curious to hear what you think!",
//         unread: false
//         },
//         {
//         from: "Tauheed Epps",
//         datetime: 1420509780000,
//         subject: "I'm different EOM",
//         message: "",
//         unread: false
//         },
//         {
//         from: "Emily Toff",
//         datetime: 1420386780000,
//         subject: "Why so serious?",
//         message: "I finally saw that movie you were talking about and really liked it! Thanks for the recommendation.",
//         unread: false
//         },
//         {
//         from: "Arielle Reinstein",
//         datetime: 1420224600000,
//         subject: "This weekend",
//         message: "Hi, are you around this weekend? Want to check out the new coffee shop that opened down the street?",
//         unread: false
//         }
// ]

$scope.unreadCheck = function(index) {
	$scope.emails[index].unread = !$scope.emails[index].unread;

};
  
}]);

home.html

<div class="email" ng-repeat="email in emails">
<a href="#/outbox/{{$index}}">
<span class="from">{{ email.from }}</span><span class="subject">{{ email.subject }}</span><span class="date">{{ email.datetime | date }}</span>
</a>
<p><button ng-click="unreadCheck($index)" class="btn-yellow btn">{{email.unread  === true ? 'unread' : 'read' }}</button></p>
</div>