AngularJS. Prevent updating ALL data in $scope - angularjs

Question

I am novice in Angular and I have a question.
I noticed that angular updates all scope data on view (am I right?), even if it has been changed only one variable (that renders on view). Is it normal ? What if I have large data on view and I want to update it only when this is data being changed.
Code for example (every time when scope.word is being modified function func is executing):
<div ng-app="myApp" ng-controller="myCtrl">
Word: <input ng-model="word">
{{func()}}
</div>
<script>
var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope) {
$scope.word = "John Doe";
$scope.func = function(){
alert("Who dared to disturb me !? >(");
};
});
</script>

Answer 1

Is it normal? - You bet it's normal, this is the whole idea.
What you're doing is not a good practice at all. However, because when you bind a function as an expression in the view, Angular doesn't "know" when it should update the expression in the view, so it updates it on every digest cycle that happens a lot! Almost every time the user interacts with the view (Click, scroll) or if anything is changed on the controller side, so you might find yourself ending up with this error.
You should bind properties to the view, not functions. Example:
angular.module('app',[]).controller('ctrl', function($scope) {
$scope.welcomeMessage = "Hi, welcome to AngularJS!";
$scope.updateMessage = function(message) {
$scope.welcomeMessage = message;
};
});
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="app" ng-controller="ctrl">
<strong>{{ welcomeMessage }}</strong>
<hr>
<input type="text" ng-model="msg">
<button ng-click="updateMessage(msg)">Update Message</button>
</div>
Note that if you know that you need to bind a property in the view only once, then you can use one time binding:
<strong>{{ ::welcomeMessage }}</strong>
Or
<strong ng-bind="::welcomeMessage"></strong>
By adding :: to the expression you prevent angular from tracking this expression after it is bound to the view the first time, and will not update it again, even if it was changed on the controller. Which is good for the performances of your app and can dramatically improve them.
Here is a working example of one-time binding: https://jsfiddle.net/hu9zcbwh/2/ (I couldn't create stack-snippet because it doesn't have angular 1.3 where this feature was first introduced)
I'm editing this with #MaximShoustin comment, that should help make this more clear and summarizes better the differences between the normal binding and one time binding:
ng-bind or {{}} generates one watcher and it will be fired after each digest cycle. On the other hand, :: expression creates watcher and cancels it once the value is not undefined
Sorry, not a native English speaker :(