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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It is a little bit outdated, but Sacha Greif's Reactivity Basics is a very quick and concise introduction to meteor's reactivity model.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, List populating via search

I am using a backemnd service (parse in this case but that doesn't really matter for this question) and wanted to simply search it. I have a textbox that upon text being entered searches the server and returns an array of matchs.
My next step is to simply display my returned objects nicely in a list. Easy enough with ng-repeat but because the view has already been loaded the UI won't update to reflect the array being loading into the list. Does that make sense?
I was wondering if there was a technique to Refresh the list and show the returned search elements, and hopefully I am not being to greedy here but doing it in a way that looks good and not clunky.
I did a lot of googling with NO luck :( any advice would be amazing.

Without any code provided it is hard to guess what is wrong. Angular has two-way binding, so view should be updated automatically after changing content of an array. If it's not, it means that you probably did something wrong in your code. I present an example code which should work in this case.
Controller
angular.module('moduleName')
.controller('ViewController', ['ViewService', ViewController]);
function ViewController(ViewService) {
var self = this;
self.arrayWithData = [];
self.searchText = "";
// ---- Public functions ----
self.searchData = searchData;
// Function which loads data from service
function searchData(searchText) {
ViewService.getData(searchText).then(function(dataResponse) {
// Clear the array with data
self.arrayWithData.splice(0);
// Fill it again with new data from response
angular.forEach(dataResponse, function(item) {
self.arrayWithData.push(item);
});
});
}
// --- Private functions ---
// Controller initialization
function _initialize() {
self.searchData(self.searchText);
}
_initialize();
}
View
<div ng-controller="ViewController as view">
<input type="text" ng-model="view.searchText" />
<input type="button" value="Search!" ng-click="view.searchData(view.searchText)" />
<!-- A simple ngRepeat -->
<div ng-repeat="item in view.arrayWithData">
<!-- Do what you want with the item -->
</div>
</div>
Conclusion
By using splice() and push() you make sure that reference to your array is not changed. If you are using controllerAs syntax (as in the example), assigning new data with '=' would probably work. However, if you are using $scope to store your data in controller, losing reference to the array is the most probable reason why your code doesn't work.

How to force knockoutjs to update UI (reevaluate bindings)

(I know there are other questions here asking the same thing; I've tried them and they don't apply here)
I have a collection being displayed by a Knockout JS foreach. For each item, the visible binding is set by call a method, based on something external to the item itself. When the externality changes, I need the UI to be redrawn.
A striped down version can be seen in this Fiddle: http://jsfiddle.net/JamesCurran/2us8m/2/
It starts with a list of four folder names, and displays the ones starting with 'S'.
<ul data-bind="foreach: folders">
<li data-bind="text: $data,
visible:$root.ShowFolder($data)"></li>
</ul>
<button data-bind="click:ToA">A Folders</button>
Clicking the button should display the ones starting with 'A' instead.
self.folders = ko.observableArray(['Active', 'Archive', 'Sent', 'Spam']);
self.letter = 'S';
// Behaviours
self.ShowFolder = function (folder)
{
return folder[0] === self.letter;
}
self.ToA = function ()
{
self.letter = 'A';
}
UPDATE:
After Loic showed me how easily this example could be fixed, I reviewed the differences between this example and my actual code. I'm using an empty object as a dictionary to toggle if an item is selected self.Selected()[item.Id] = !self.Selected()[item.Id];
The object being changed is already an observable. I assumed that Knockout didn't realize that the list is dependent on the external observable, but it does. What Knockout was missing was that the observable was in fact changing. So, the solution was simply:
self.Selected()[item.Id] = !self.Selected()[item.Id];
self.Selected.notifySubscribers();

Here's what I came up with:
What you have to understand is that Knockout is only "answering" to data changes in observables. If an observable changes, it will trigger every object that uses it. By making your self.letter an observable. You can simply change it's value and uses it somewhere like self.letter() and it will automagically redraw when needed.
http://jsfiddle.net/2us8m/3/
function WebmailViewModel() {
// Data
var self = this;
self.folders = ko.observableArray(['Active', 'Archive', 'Sent', 'Spam']);
self.letter = ko.observable('S');
// Behaviours
self.ShowFolder = function (folder)
{
return folder[0] === self.letter();
}
self.ToA = function ()
{
self.letter('A');
}
};
ko.applyBindings(new WebmailViewModel());
In case you have complex bindings, like storing an object inside an observable. If you want to modify that object you have multiple possible choices.
self.Selected()[item.Id] = !self.Selected()[item.Id];
You could change it to this by making everything "observables" but if my memory is right, it can become complicated.
self.Selected()[item.Id](!self.Selected()[item.Id]());
I remember I had one similar issue where I had dependency problem where I had to update a country, region, city. I ended up storing it as list inside an observable to prevent update on individual element change. I had something like this.
var path = PathToCity();
path[0] = 'all';
path[1] = 'all';
PathtoCity(path);
By doing this, the change would be atomic and there will be only one update. I haven't played a lot with knockout for a while. I'm not sure but I do believe that the last time I worked with knockout, it was able to "optimize" and prevent to redraw the whole thing. But be careful because if it is not able to guess that you didn't change many thing, it could redraw the whole observable tree (which could end up pretty bad in term of performance)
In your example, we could use the same behaviour with my modified example:
http://jsfiddle.net/2us8m/4/

KO ObservableArray update breaks when binding with .sort

I'm sorting my ObservableArray in the markup thusly, but for some reason, when I push a new object to the pages ObservableArray, this does not update.
//store.get('pages') returns an ObservableArray
<!-- ko foreach:store.get('pages').sort(function (l , r ) { return l.pageNumber() < r.pageNumber() ? -1 : 1}) -->
<markup/>
<!--/ko-->
However, when I remove the sort call, it catches the array change just fine.
Like so,
//works fine, updates when item pushed to observableArray
<!-- ko foreach:store.get('pages') -->
<markup/>
<!--/ko-->
Any idea for a simple workaround?
Edits:
Tried using valueHasMutated(), doesn't force an update either.
Workaround:
I ended up moving the sort call into a subscription on the observableArray, and it seems to be working fine now, not sure why though.

store.get returns an observableArray but store.get(...).sort(...) returns an array. You're effectively making a one way binding like this:
<div data-bind="foreach: ['foo', 'bar']"></div>
Also, although you bind a returned value of a function call, to me it has a code smell that you're coupling your business logic with your view logic. You have something like this:
// View
<div data-bind="foreach: $root.get()"></div>
// Javascript
function ViewModel () {
var self = this;
self.get = function () {
return ko.observableArray();
};
}
And it works, but from your view, it's unclear what you're doing. I think a better solution would be:
// View
<div data-bind="foreach: stores"></div>
// Javascript
function ViewModel () {
var self = this;
self.stores = ko.observableArray();
self.get = function () {
var arr = ["foo", "bar"];
stores(arr.sort(...));// When you do this, KO updates the foreach binding this is bound to
return stores;// not that you need to, you can access it from the viewModel.
};
}
Glad you found a workaround but take a minute and plan out your HTML binding structure. It's the first place I start when I'm creating a new view and it drives how I structure my ViewModel.

How to make a DOM element update after an object it depends on changes in meteor?

I have an object in an array
var
sidelist = [
{
name:"MURICA",
types:[...]
}
];
I have a box that displays the object's name. Then I have a text field and a button. On button press the object's name gets set to text field value. But I don't know how to make the name in the box change accordingly.
As I understand putting the object in a session variable is not an option since I will not be able to modify properties of objects inside of it without resetting the whole session var. I tried it and failed.

html
<template name="asdf">
{{#with object}}
<div>{{name}}</div>
{{/with}}
</template>
js
Template.asdf.object = function() {
return Objects.findOne(...);
};
EDIT
I think I've got your question wrong, sorry. If you have a value in memory that you'd like to change and have the DOM updated, use dependencies:
html
<template name="asdf">
{{property}}
</template>
js
var property;
// Create new dependency object that will manage refreshing property value:
var _dep = new Deps.Dependency;
updateProperty = function(value) {
property = value;
// Whenever you change value of the property, call changed() function:
_dep.changed();
};
Template.asdf.value = function() {
// Within reactive function, call depend() to rerun the function
// each time the value is changed:
_dep.depend();
return value;
};

How about a different and in my opinion simpler solution - using a local collection for your data.
I am not sure exactly why do you keep that sort of data into an array, but if it is because you only need it on the client then you can instead create a local collection and have all the reactivity benefits without writing all that code for making the array reactive. The data stored in a local collection is never sent to the server, so no communication or storage overhead.
You'd do it like that:
Sidelist = new Meteor.Collection(null);
[EDIT] Put the above line in your client-side-only part of the code.
Notice the null parameter. This will give you a collection that is only stored on the client and is a regular Meteor reactive source. Then you go about using it in your code and html just as you would a normal collection.
Hope that helps.