Programmatically apply classes to angularjs form - angularjs

Question

I have an angular directive to facilitate the adding of bootstrap classes at runtime to streamline the need to apply "form-group", "control-label" and "form-control". This works perfectly as long as I don't try to include multiple levels at once, meaning that I cannot seem to make this work to include multiple divs in "form-group. I have attached the code, raw HTML and processed HTML for review to see if someone might have some insight into how I might modify to make this tool meaningful.
Directive:
(function () {
"use strict";
angular.module("ppac")
.directive("formfix", formfix);
var addClasses = function (element) {
var input = element.querySelector("input, textarea, select");
var type = input.getAttribute("type");
if (type !== "checkbox" && type !== "radio") {
input.classList.add("form-control");
}
var label = element.querySelector("label");
label.classList.add("control-label");
element.classList.add("form-group");
};
function formfix() {
return {
restrict: "A",
link: function (scope, element) {
addClasses(element[0]);
}
}
}
})();
HTML Form:
<form name="contactForm" ng-submit="model.submit()" novalidate>
<div class="form-horizontal">
<div formfix>
<label for="firstName" class="col-md-2">First Name</label>
<div class="col-md-3">
<input type="text" name="firstName" id="firstName" ng-model="model.contact.firstName" />
</div>
<label for="lastName" class="col-md-2">Last Name</label>
<div class="col-md-3">
<input type="text" name="lastName" id="lastName" ng-model="model.contact.lastName" />
</div>
</div>
</div>
</form>
Processed HTML:
<form name="contactForm" ng-submit="model.submit()" novalidate="" class="ng-pristine ng-valid">
<div class="form-horizontal">
<div formfix="" class="form-group">
<label for="firstName" class="col-md-2 control-label">First Name</label>
<div class="col-md-3">
<input type="text" name="firstName" id="firstName" ng-model="model.contact.firstName" class="ng-pristine ng-valid form-control ng-empty ng-touched">
</div>
<label for="lastName" class="col-md-2">Last Name</label>
<div class="col-md-3">
<input type="text" name="lastName" id="lastName" ng-model="model.contact.lastName" class="ng-pristine ng-untouched ng-valid ng-empty">
</div>
</div>
</div>
</form>

Answer 1

You can use ng-class to add class dynamically as the document says
The ngClass directive allows you to dynamically set CSS classes on an
HTML element by databinding an expression that represents all classes
to be added.
Reference
https://docs.angularjs.org/api/ng/directive/ngClass