Why doesn't Angular.js update View on Socket.io event?

Question

Angular

Good day!
Why doesn't Angular update the DOM on a Socket.io event? Although if you output console.log data, then the date is not undefined.
CoffeeScript:

do (window, angular, io)->
    adminApp = angular.module('adminApp', [])
    socket = io.connect '/', {
        path: '/admin/socket.io'
    }

    adminApp.controller 'ProgressCtrl', [
        '$scope'
        ($scope) ->
            $scope.stats = {
                cpu:
                    percent: 10
                memory:
                    percent: 70
            }

            socket.on 'server:stats', (data) ->
                $scope.stats.percent = data.os.percent * 100
    ]

Answer 1

Because the socket works asynchronously and angular doesn't know about the change of the variable. In order for angular to check this variable, you need to force it to do so, for this you can either call the $scope.$apply() or $scope.$digest() function or wrap the code that changes the data in a construct

$timeout(function(){
// тут код
})

But there is one problem with using $scope.$apply() and $scope.$digest() functions, if digest is already running, angular crashes, so I advise you to use $timeout

Answer 2

Good day!
You need to put scope.$watch() on property changes in scope. See the documentation for an example https://docs.angularjs.org/api/ng/type/$rootScope.Scope , section $watch