Djambulat,
<!DOCTYPE html>
<html lang="en" ng-app="app">
<head>
<style type="text/css">
div span{
cursor: pointer;
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.6/angular.min.js"></script>
</head>
<body>
<main ng-controller="AppController">
<div >{{ inputstring }}</div>
<div>
<span ng-repeat='b in letter' ng-click="getLetter(b)"> {{b}}</span>
<span ng-click="inputstring = inputstring.slice(0,-1)"> ↵</span>
</div>
</main>
<script>
(function() {
'use strict';
angular
.module('app', [])
.controller('AppController', ['$scope', function($scope) {
$scope.letter = 'qwerty';
$scope.inputstring = "";
$scope.getLetter = function(letter) {
$scope.inputstring += letter ;
};
}]);
})();
</script>
</body>
</html>