How to Display the first 20 messages in the DB - arrays

Question

I found this code in the internet, it functions as a message box. The code works perfectly fine. However, it display all the messages stored in the file message.db.
My question is, how can I make it display only the last 20 posted messages? I'm sorry for asking this. I have no knowledge about programming. I appreciate any help...
Here is the snippet of the code:
<div class="container" ng-controller="MessageBoardCtrl">
<form>
<input type="email" placeholder="Email Address" ng-model="email" required/>
<textarea placeholder="Advertise your link here for Free..." rows="5" style="width:90%" ng-model="message" required=""></textarea>
<button class="btn btn-primary" ng-click="sendMessage()">Post</button>
</form>
<p>{{item.message}}</p>
<script>
function MessageBoardCtrl($scope, $http, $timeout) {
$scope.items = [];
$scope.message = '';
$scope.email = '';
$scope.lastTime = 0;
$scope.refreshMessages = function() {
$http.get('../templates/faucet.php/messages?time=' + $scope.lastTime).success(function(data) {
for(id in data) {
item = data[id];
$scope.items.unshift(item);
if($scope.lastTime<item.time)
$scope.lastTime = item.time;
}
});
}
$scope.sendMessage = function() {
if(!$scope.message)
return;
$http.post('../templates/faucet.php/add_message', {message: $scope.message, email: $scope.email}).success(function() {
$scope.message = '';
$scope.refreshMessages();
});
}
$scope.periodicRefresh = function() {
$scope.refreshMessages();
$timeout($scope.periodicRefresh, 5000, true);
}
$scope.periodicRefresh();
}
</script>
I found this function to limit the result:
function limitToFilter(){
return function(array, limit) {
if (!(array instanceof Array)) return array;
limit = int(limit);
var out = [],
i, n;
// check that array is iterable
if (!array || !(array instanceof Array))
return out;
// if abs(limit) exceeds maximum length, trim it
if (limit > array.length)
limit = array.length;
else if (limit < -array.length)
limit = -array.length;
if (limit > 0) {
i = 0;
n = limit;
} else {
i = array.length + limit;
n = array.length;
}
for (; i<n; i++) {
out.push(array[i]);
}
return out;
}
}
Now, I just need help on how to combine them together to make the script work. I hope someone can help. I really do not have any idea... Thanks.