Automatic _.bindAll() in backbone.js - javascript

Is there a way to automatically do an _.bindAll for a backbone.js object?
I was talking to someone a while ago and they said that there was, but I have no idea where to start looking.
Example:
var TheView = Backbone.View.extend({
initialize: function() {
// HOW CAN I AVOID HAVING TO DO THIS?---->
_.bindAll(this,'render','on_element_01_click', 'on_element_02_click');
},
events: {
'click #element_01': 'on_element_01_click',
'click #element_02': 'on_element_02_click',
},
render: function(){
return this;
},
on_element_01_click: function(){
},
on_element_02_click: function(){
}
}

Do this instead:
_.bindAll(this);
Will bind ALL functions in this view.

I've since learned of a easier technique if you want to build bindAll in to your views (which is handy for things like AJAX callback methods that aren't auto-bound the way event handlers are). Basically you just override the constructor to perform the auto-binding.
var BoundModel = Backbone.Model.extend({
constructor: function() {
Backbone.Model.apply(this, arguments);
if (this.boundMethods) {
_(this).bindAll.apply(this, this.boundMethods);
}
}
})
var SubclassOfBoundModel = Backbone.Model.extend({
boundMethods: ['handleFetchResponse'],
initialize: function () {
this.model.on('sync', this.handleFetchResponse);
}
handleFetchResponse: function() {
// this function is bound to the model instance
}
})
Of course if you just wanted to bind all your methods you could leave out the "boundMethods" part and just have:
constructor: function() {
Backbone.Model.apply(this, arguments);
_(this).bindAll();
}

I tried doing this myself and I was able to get it working with something like this:
function bindOnExtend(clazz) {
var originalExtend = clazz.extend;
clazz.extend = function() {
var newSubClass = originalExtend.apply(this, arguments);
var originalInitialize = newSubClass.prototype.initialize;
newSubClass.prototype.initialize = function() {
// The constructor will get broken by bindAll; preserve it so _super keeps working
var realConstructor = this.constructor;
_.bindAll(this);
this.constructor = realConstructor;
originalInitialize.apply(this, arguments);
};
return bindOnExtend(newSubClass);
};
return clazz;
}
var BoundModel = Backbone.Model.extend();
bindOnExtend(BoundModel);
var BoundView = Backbone.View.extend();
bindOnExtend(BoundView);
However, I wouldn't recommend it. Doing that will make closures for every single method on every single model/view/whatever you instantiate. Not only does that add a slight increase in overall memory usage, it also opens up the possibility of memory leaks if you're not careful. Furthermore, it makes your stacktraces several lines longer, as they have to wind through bindOnExtend.
In my experience, having to do "_.bindAll(this, ..." is worth the trouble because:
1) it makes my code more clear/obvious to anyone coming after me
2) it encourages me to qualify my bindAll, instead of just using the 1-arg form
3) I hate wading through long stacktraces
But, if you want it the above code should work.

Related

Backbone: Subview depends on another subview being rendered

I have a Backbone SAP which has two subviews within its main App view. These are interdependent: the top one dispalys a music score rendered using Vexflow (Javascript music notation package), and the other below it displays an analysis of the score, also using Vexflow but with some extra objects (text, lines, clickable elements, etc).
The main problem I have is that a lot of the data I need for the analysis view doesn't come into existence until the score view has been rendered. For example, the x coordinate of a musical note is only available after the note has been drawn (the same isn't true of the y coordinate). Below is (in schematic terms) how my app view is set up:
var AppView = Backbone.View.extend({
//...
initialize: function() {
this.scoreView = new ScoreView();
this.analysisView = new AnalysisView({
data: this.getAnalysisData()
});
},
render: function() {
this.scoreView.render();
this.analysisView.render();
return this;
},
getAnalysisData: function() {
// Performs anaysis of this.scoreView,
// and returns result.
}
});
My work around is to move the analysis view setup into the render method, after the score view has been rendered. I dislike doing this, as the getAnalysisData method can be quite expensive, and I believe the render method should be reserved simply for rendering things, not processing.
So I'm wondering if - since there doesn't seem to be a Vexflow solution - there is a Backbone pattern that might fix this. I am familiar with the 'pub/sub' event aggregator pattern for decoupling views, as in:
this.vent = _.extend({}, Backbone.Events);
So on this pattern the analysis view render method subscribes to an event fired after the score view is rendered. I'm not sure how this would alter my code, however. Or perhaps use listenTo, like this:
// Score subview.
var ScoreView = Backbone.View.extend({
initialize: function() {
this.data = "Some data";
},
render: function() {
alert('score');
this.trigger('render');
}
});
// Analysis subview.
var AnalysisView = Backbone.View.extend({
initialize: function(options) {
this.data = options.data;
},
render: function() {
alert(this.data);
return this;
}
});
// Main view.
var AppView = Backbone.View.extend({
el: "#some-div",
initialize: function() {
this.scoreView = new ScoreView();
var view = this;
this.listenTo(this.scoreView, 'render', this.doAnalysis); // <- listen to 'render' event.
},
render: function() {
this.scoreView.render();
return this;
},
doAnalysis: function() {
this.analysisView = new AnalysisView({
data: this.getAnalysisData()
});
this.analysisView.render();
},
getAnalysisData: function() {
return this.scoreView.data;
}
});
Of course, the analysis step is still effectively being done 'during' the render process, but this seems a better pattern. It seems more like the Backbone way of doing things. Am I right? Or am I missing something?
Edit: I dont necessarily have to create the analysis view in the doAnalysis, I could still do that in the main view initialize (at the moment I'm not). But doAnalysis has to run after the score view has rendered, otherwise it cannot access the relevant score geometry information.

Trouble while accessing to a method

I'm beginning to use jquery and Model View ViewModel and I encounter a problem with the utilisation of this with the Event Handler Attachment : on().
My first class is TicTacToeModel which manipulates a TicTacToe game in memory :
var TicTacToeModel = function () {
Observable.call(this);
this.grid = new Array(3);
for (let i = 0; i < this.grid.length; ++i) {
this.grid[i] = new Array(3);
}
};
//Some prototype function
//...
I have another class, TicTacToeController which depends on the first class and which manages the graphic part of the game with a manipulation of the DOM :
var TicTacToeController = function(game, selector) {
this._element = $(selector);
this._model = game;
this._template = Handlebars.compile(view);
this.addListeners();
this.render();
};
(declaration of game : game = new TicTacToeModel();)
So in my second class I have this function :
TicTacToeController.prototype.addListeners = function() {
this._model.on('change', this.render, this);
this._model.play(0,0);//works
this._element.on('click', "td", function() {
this._model.play(0,0);//doesn't work
});
};
And I would like to call the play() function in the cell (0,0) (the function play updates the game in memory) when I click on the cell in my graphic interface but I cannot do it in the .on(). But that seems to be working outside of the .on() function so I suppose a bad utilisation of this causing the problem.
You need to use bind like this.
Change this:
this._element.on('click', "td", function() {
this._model.play(0,0);//doesn't work
});
to:
this._element.on('click', "td", function() {
this._model.play(0,0); //should now work
}.bind(this));
You are not in the same scope, it's not the same this variable you are employing when calling the play method.
A dirty workaround could be
let _model = this._model
this._element.on('click', "td", function() {
_model.play(0,0);//work!
});
But as said it's a dirty workaround, maybe someone else could explain but basically think this produces a memory leak. Maybe the solution would be to use a method in the same class and pass the instance to the click method, kind of:
TicTacToeController.prototype.click = function() ...
...
this._element.on('click', "td", this.click);
Think this should do the trick, but I must admit I'm not a js expert.

Knockout subscribe/event type system without observable?

I want to make use of the subscribe() function of knockout js to manually trigger an event at a certain point.
I could make an observable() and everytime put a GUID in there to trigger the scubscribe.
Is there a cleaner way within Knockout js to have a typical event-like structure?
Edit
Ok, apparently I can use observable.valueHasMutated() - might already a a bit cleaner that using a GUID.
Example
This is the behaviour that I'm looking for:
function Car()
{
var self = this;
self.onOpenDoor = ko.observable();
self.openDoor = function()
{
// using an observable / valueHasMutated for this feels a bit hacky
// is there an other way to use the underlying subscribe() system?
self.onOpenDoor.valueHasMutated();
}
}
var car = new Car();
// multiple subscribers
car.onOpenDoor.subscribe(function()
{
console.log('Do something');
})
car.o**nOpenDoor.subscribe(function()
{
console.log('Do something else');
})
car.openDoor();
I am aware this is not the default 'knockout' way to do stuff - that is not what this question is about.
Update
After #RoyJ's reference to Niemeyer's blog I went for this solution:
function Car()
{
var self = this;
self.onOpenDoor = new ko.subscribable();
self.openDoor = function()
{
self.onOpenDoor.notifySubscribers();
}
}
Update If you're just looking for clarity, you can use notifySubscribers instead of valueHasMutated. You might want to take a look at the base type of observables, ko.subscribable.
I would do it like this:
var vm = {
///...definitions...
openCount: ko.observable(0),
openDoor: function () {
vm.openCount(vm.openCount()+1);
}
};
vm.openCount.subscribe(function () {
///...do something
});
vm.openCount.subscribe(function () {
///...do something else
});
ko.applyBindings(vm);
Demo http://jsfiddle.net/uoqdfhdb/2/

How to call a function of a parent class from another function in jquery

I guess that's the simple question. I'm new in js, especially in Backbone.js.
All I want to know is how I can refer to my function inside jquery function.
getLanguages: function() {
...
return languages;
},
render: function() {
...
$("input[type='checkbox']").bind("change", function() {
// todo: getLanguages
});
}
I tried to get languages via this but, of course, I got checkbox in this case.
Edit:
It's so simple. Many thanks to all!!!
This is a classic problem in Javascript. You need to reference this inside a callback, but this changes to the element being bound to. A cheap way to do it:
render: function() {
var that = this;
$("input[type='checkbox']").bind("change", function() {
that.getLanguages();
});
}
that will stay defined as the this that render is defined on.
However, you’re using Backbone, and it has more suitable ways to handle this situation. I don’t know the name of your Backbone.View class, but here’s an example adapted from the documentation:
var DocumentView = Backbone.View.extend({
events: {
"change input[type='checkbox']": "doSomething"
},
doSomething: function() {
this.getLanguages(); # uses the correct this
}
});
Calling bind inside render is not The Backbone Way. Backbone views are made to handle event delegation without the unfortunate need to pass this around.
Save this object before bind change event in the scope of render function.
render: function() {
var CurrentObj = this;
$("input[type='checkbox']").bind("change", function() {
CurrentObj.getLanguages();
});
}
You can save the appropriate object into a local variable so from the event handler, you can still get to it:
getLanguages: function() {
...
return languages;
},
render: function() {
...
var self = this;
$("input[type='checkbox']").bind("change", function() {
var lang = self.getLanguages();
...
});
}

JavaScript: How to bind a method?

JSFiddle: http://jsfiddle.net/M2ALY/3/
My goal is to make a module that I can use and distribute. Therefore I must not pollute the global namespace. The module I'm making is also going to be used multiple times on one web page. That's why I chose to use OOP, but this introduced a problem.
I want my object to bind a function to be run when the user clicks an element in the DOM. In this simplified example I made, I want an alert box to pop up when the user clicks a paragraph. As an example, one of the things I need in the real project I'm working on is: The user clicks a canvas, the function figures out where the user clicked and saves it to this.clientX and this.clientY.
Instead of doing
this.bind = function() {
$("p1").bind('click', function() {
// code here
});
}
I figured it would work if I did:
this.bind = function() {obj.codeMovedToThisMethod()}
The problem is that this isn't a good design. Inside the "class" you shouldn't need to know the name of the object(s) that is going to be made of this "class". This doesn't get better when I'm making multiple objects of the "class"...
So I figured I could do
$("p1").bind('click', function(this) {
// code here
});
}
But it didn't work because sending this into the function didn't work as I thought.
How should I solve this problem?
Here is a simplified sample problem. (Same as JSFiddle.)
var test = function() {
this.alert = function() {
alert("Hi");
}
this.bind = function() {
$("#p1").bind('click', function() {
obj.alert();
});
}
}
window.obj = new test();
obj.bind();
// What if I want to do this:
var test2 = function() {
// Private vars
this.variable = "This secret is hidden.";
this.alert = function() {
alert(this.variable);
}
this.bind = function() {
$("#p2").bind('click', function(this) {
obj2.alert();
this.alert();
});
}
}
window.obj2 = new test2();
obj2.bind();​
Thanks!
Read MDN's introduction to the this keyword. As it's a keyword, you can't use it as a parameter name.
Use either
this.bind = function() {
var that = this;
$("#p2").on('click', function(e) {
that.alert();
// "this" is the DOM element (event target)
});
}
or $.proxy, the jQuery cross-browser equivalent to the bind() function:
this.bind = function() {
$("#p2").on('click', $.proxy(function(e) {
this.alert();
}, this));
}

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