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Angular - recalculate a variable on every change

I have a variable that stores the available cars at any moment. Is there a way to automatically re-evaluate this function on every change?
Just using this.carFactory.available in this case is not a solution, because this example I'm showing is simplified - the real calculation in my project is alot more complex.
calculateAvailableCars(){
this.carFactory.available.forEach(function(item){
this.availableCars.push(car.id);
}.bind(this));
}
How could I do this in Angular 2? In Angular JS there was the possibility to $watch a function.
I could of course manually call this function everytime something changes, but it would be nice not to have to call this function in every part of the application that can change the data.

Using template function reference with auto change detection
You can use this function output on template:
carOutput(): cars[] {
this.calculateAvailableCars()
return this.availableCars;
}
and use output on template:
<p>My car ratio is {{ carOutput() }} </p>
However this will trigger very aggressive change detection strategy on this variable. This solution is the simpliest one, but from engineering perspective rather worst: consumes tons of unnecessary function calls. One note, that hosting element must not be set to detect changes onPush.
Separate data model to parent component and pass as property to child
You can store car list display in separate component, and pass new car array as input property to this component:
<car-display [cars]="availableCars"></car-display>
Then you can set changeDetetcion policy in this component to onPush, and each time input property bind to availableCars will change, <car-display> will re-render.
If update relays on some host binding
If some external host action is triggering new cars calculation, then hostBinding may help:
#hostListener(`hover`) recalculateCars() {
this.calculateAvailableCars()
}
And finally, (because you describe your use case quite cryptically, without many details, thus I'm scratching all possible scenarios) if some external component action shall trigger re-calculation, you can hook to ngLifecycle ngOnChanges() if for example external input property change shall re-trigger cars calculation.
In other words and summing all that up, it depends who and from where triggers changes, that shall re-trigger available cars recalculation.
And very important, see an answer from #chiril.sarajiu, because what we are trying to work around here can be handled automatically by single observable. This requires additional setup (service, provide observable to components, e.c.t.) but it's worth.
--- EDIT ---
If each variable change shall retrigger data
As OP clarified, that changes are related with model bound to component. So another option with mentioned by #marvstar is using set, where each model variable change will retrigger fetching function:
modelSchangeSubject: Subject<Model> = new Subject<Model>();
ngOnInitt() {
this.modelSchangeSubject
.subscribe((v: Model) => {
this.calculateAvailableCars()
})
}
/* Rest of controller code */
set modelBounded(v: Model) {
this.modelSchangeSubject.next(v);
}

You need RxJS. What you do is you create a data service, which will store an Observable (in my case a BehaviorSubject, which is mostly the same, but in my case I start with a value).
export class DataService {
private dataStorage$ = new BehaviorSubject(null); //here is the data you start with
get getDataStorage() {
return this.dataStorage$.asObservable(); // so you won't be able to change it outside the service
}
set setDataStorage(data: any) {
this.dataStorage$.next(data);
}
}
Then you subscribe to this data changes everywhere you need to:
constructor(private dataService: DataService){}
ngOnInit() {
this.dataService.getDataStorage.subscribe((data) => this.calculateAvailableCars(data));
}
calculateAvailableCars(){
this.carFactory.available.forEach(function(item){
this.availableCars.push(car.id);
}.bind(this));
}
Read more about best practices of using RxJS in Angular, as there can be quite a bit of pitfalls and problems.

Try using setter and getter.
private _YourVariable:any;
public set YourVariable(value:any){
this._YourVariable = value;
//do your logik stuff here like. calculateAvailableCars
}
public get YourVariable():any{
return this._YourVariable ;
}

Refresh the parent component view in Angular 4

I have got 2 components, let's say, Component A is a list view and Component B is a details view. Each row from the list view is clickable and will redirect to Component B upon clicking.
Component B allows editing and saving the details. I have added a Back button to Component B to allow me to go back to the list view.
But the problem I am having is that I can't see the updated list view and have to manually refresh the browser, and then I can see the updated list there.
I have tried directly using window.location and it works but really I don't prefer this approach.
public back() {
window.location.assign('/listview');
}
I wonder if there's any better way to solve this problem?
Update:
public onSelected(model: MyModel) {
const detailsViewUrl = `/detailsview/${model.id}`;
this._router.navigateByUrl(detailsViewUrl );
}

You can just emit an #Output EventEmitter with a method on Parent that looks in the event for a change with a variable stored in the component like this:
#Output someOutput: EventEmitter = new Event Emitter<any>;
HTML:
<b-component (someOutput)=getOutput($event)></b-component>
AComponent:
getOut(event){
let output = event;
if(this.something != output){
this.ngOnDestroy(); // or something that you can use to make it
}
That should work as intended.

It sounds like this is an issue with Angular's change detection when changing the contents of an array. See here:
Angular 2: How to detect changes in an array? (#input property)
The solutions in this questions should work but an easy way I have used in the past to force changes in an array to be recognised by Angular is to reassign the array after making the changes:
myArray = [...myArray];

use following routing fuction on back button click
public back() {
this._router.navigateByUrl('/listview')
}
or
public back() {
this._router.navigate('/listview')
}

Try this,
Just called the list view again internally and hit db at same time so updated values will be displayed in the list view.
calling the route by using below:
this.router.navigate(['/listview']);

Seems like a change detection issue, there are some ways to manually trigger change detection like so:
Inject ChangeDetectorRef.
Call it when you go back like so:
public back() {
ChangeDetectorRef.detectChanges()
}
Refer to this: Triggering change detection manually in Angular

Reactively call a js function/event with meteor.js

I'm new to meteor.js. Still getting used to it.
I get how templates update reactively according to the cursor updates on the server, like this:
{{#if waitingforsomething.length}} Something Happened! {{/if}}
This is good to display elements on the page, updating lists and content. Now, my question is: what if I want to call some javascript or fire some event when something gets updated reactively? What would be the right way to do it with meteor.js?

Anything inside Tracker.autorun or template instance this.autorun runs with changes in reactive data sources inside these autoruns.
Reactive data sources are ReactiveVar instances, db queries, Session variables, etc.
Template.myTemplate.onCreated(function() {
// Let's define some reactive data source
this.reactive = new ReactiveVar(0);
// And put it inside this.autorun
this.autorun(() => console.log(this.reactive.get()));
});
Template.myTemplate.events({
// Now whenever you click we assign new value
// to our reactive var and this fires
// our console.log
'click'(event, template) {
let inc = template.reactive.get() + 1;
template.reactive.set(inc);
}
});

It is a little bit outdated, but Sacha Greif's Reactivity Basics is a very quick and concise introduction to meteor's reactivity model.
Basically, you have what's called reactive computations, code that observes special data objects (sessions, subscriptions, cursors, etc.) and gets executed whenever any of these reactive sources changes.
This is exposed via the Tracker API

Computation works pretty well for me:
Template.myTemplate.onRendered(function() {
this.computation = Deps.autorun(function () {
if (something) {
$(".reactive").html("Something Happened!");
}
});
});
Template.myTemplate.destroyed = function(){
if (this.computation){
this.computation.stop()
}
};
I Hope this helps.

Ionic and Angularjs - Update/Refresh View from Controller

The usual start to these, I am new to both Ionic and Angularjs. I am developing an Ionic app which at it's heart is very simple. We show a list of classes(sessions), the person clicks on an icon to book the class then the icon changes to allow them to cancel the class. We also update the card to show the number of places remaining in each session on the day.
I have the code working to add and remove a person to and from a class but I am not sure how to update the template view from within the controller.
The controller code is pretty simple
// Check Person in to session.
$scope.addCheckIn = function(schedule){
var promise = sessionDataService.checkinSession(schedule.sessionID);
promise.then(function(data){
// Update (refresh) Schedule Details
// NOT SURE WHAT TO PUT HERE??
});
};
I have tried a number of different approaches including
Refreshing the $state and calling doRefresh and even calling the original controller methods to populate the cards again but the view won't update unless I physically click between states on the screen
//$state.go('app.schedules', {}, {reload: true});
//$scope.doRefresh();
//getScheduleData(formatDate(selectedDate), formatDate(selectedDate), 'true');
I have also looked at $scope.apply and $scope.timeout but I am not sure if this is taking me further from the real solution
What is the correct way to update the view after an update? Should it be after the promise.then in the controller or should I call a service and update everything.
Any tips on what is the best way to do this and a point in the right would be really appreciated.
Thanks everyone.

In your promise, you should add the data to the scope.
$scope.scheduledetails = data;
Then in your template, you will be able to access the object scheduledetails from the controller with AngularJS brackets to bind the data to the HTML.
<h1>{{scheduledetails.title}}</h1>
<p>Details : {{scheduledetails.details}}</p>
AngularJS should take care of refreshing what is needed without having to call any method or anything.
Full example
Controller
$scope.addCheckIn = function(schedule){
var promise = sessionDataService.checkinSession(schedule.sessionID);
promise.then(function(data){
$scope.scheduledetails = data;
});
};
Template
<h1>{{scheduledetails.title}}</h1>
<p>Details : {{scheduledetails.details}}</p>

AngularJS - Router UI - Defining a wildcard parented state

Fellas, Fellaaas.
I'm writing from my phone so please excuse me for anything misleading or unclear.
In my app there's a state that can be inherited from any other parent state, called "deals/:dealId:".
As of now, I have to define the same state over and over again for any other parent state available, so it could be accessible from any URL on the app.
For example: the parent state "dashboard" has a child state "parent.dashboard.deals", so is another state - "parent.lookup.deals", and so on.
While googling for a solution I found an example on plunkr using a parent state variable definition to create a wildcard'ed state environment:
.state(currentState+".deals").
"Boy oh boy", I thought to myself. That's exactly what I need. Well, not.
I was testing it and it on a static "currentState" variable and it worked just fine, thought all I had left to do was to dynamically change the currentState variable between parent states switchings.
It appears that when angular is generating the routes for the first time on loading, it takes the default "currentState" var as a string and defines that state static. So, even though I'm changing the default "currentState" var between route changes, the state is only available to the first generated state definition.
Thank you.

I've posted a feature request on GitHub, just in case I'm the first one in the need for this scenario - or there isn't a proper solution meanwhile for this problem:
github.com/angular-ui/ui-router/issues/1014
Anyhow,
I managed this problem by looping through the parent states and attaching the static child state to them, instead of defining them manually:
angular.forEach(states, function(stateOptions,stateName) {
$stateProvider.state(stateName, stateOptions.options);
if (stateOptions.defaultState){
var dealStateName = stateName+'.deals';
console.log(dealStateName);
$stateProvider.state(dealStateName,{
url: (stateName=='parent.dashboard') ? "deals/:dealId" : "/deals/:dealId",
views:{
'fsItem#parent':{
templateUrl: "/static/html/fsItems/dealNewD.html",
controller: 'dealCtrl',
}
}
});
}
});

The question isn't quite clear, but it sounds like you want a state variable(s) that persists between route changes. I'd suggest using a factory or service. Take a look at Sharing a Variable Between Controllers in AngularJS.