How to transfer some letters to uppercase dynamically in angular - html

Question

i got a problem when i was making to capitalize dynamically. In my code i can capitalize any letters but it is not dynamic,the program should guess which letter should it capitalize.For example some text comes from JSON and there should be some comparing that checks texts letters and users inputed letters and then he should guess which letter he must capitalize. if there is some solution for this, please tell me. here is my code :
index.html
<textarea id="fieldId" class="textarea" style="resize: none" cols="30" row="2" ui-mask="{{typetext}}" ng-model="model" data-ng-trim="fasle" ng-trim="false" ng-focus="expression">
</textarea>
scipt.js, thats what i was trying to do.
link: function(scope, iElement, iAttrs, controller) {
controller.$parsers.push(function(inputValue) {
var transformedInput = '';
if (inputValue) {
for (var i = 0; i < inputValue.length; i++) {
if (i === 0 || i === 5) {
transformedInput += inputValue.charAt(i).toUpperCase();
} else {
transformedInput += inputValue.charAt(i).toLowerCase();
}
}
}
if (transformedInput != inputValue) {
controller.$setViewValue(transformedInput);
controller.$render();
}
return transformedInput;
});
})
and controller
app.controller('myController', ['$scope', '$document', function($scope, $document) {
$scope.typetext = "Some Text";
$document.on('keydown', function(e) {
if (e.which === 8 && e.target.nodeName !== "INPUT") {
e.preventDefault();
}
});
}])