If you don't want to put CSS class names into Controller like I do, here is an old trick that I use since pre-v1 days. We can write an expression that evaluates directly to a class name selected, no custom directives are necessary:
ng:class="{true:'selected', false:''}[$index==selectedIndex]"
Please note the old syntax with colon.
There is also a new better way of applying classes conditionally, like:
ng-class="{selected: $index==selectedIndex}"
Angular now supports expressions that return an object. Each property (name) of this object is now considered as a class name and is applied depending on its value.
However these ways are not functionally equal. Here is an example:
ng-class="{admin:'enabled', moderator:'disabled', '':'hidden'}[user.role]"
We could therefore reuse existing CSS classes by basically mapping a model property to a class name and at the same time keep CSS classes out of Controller code.
ng-bind has one-way data binding ($scope --> view). It has a shortcut {{ val }}
which displays the scope value $scope.val inserted into html where val is a variable name.
ng-model is intended to be put inside of form elements and has two-way data binding ($scope --> view and view --> $scope) e.g. <input ng-model="val"/>.
Best Answer
AngularJS form elements look for the
requiredattribute to perform validation functions.ng-requiredallows you to set therequiredattribute depending on a boolean test (for instance, only require field B - say, a student number - if the field A has a certain value - if you selected "student" as a choice)As an example,
<input required>and<input ng-required="true">are essentially the same thingIf you are wondering why this is this way, (and not just make
<input required="true">or<input required="false">), it is due to the limitations of HTML - therequiredattribute has no associated value - its mere presence means (as per HTML standards) that the element is required - so angular needs a way to set/unset required value (required="false"would be invalid HTML)