I use jQuery for some time, but that is usually very simple jQuery. I just watched some video tutorial in which the author uses something called Pub Sub Pattern. I've never heard of it before, so I have searched on Stackoverflow and Google for explanations:
Why would one use the Publish/Subscribe pattern (in JS/jQuery)?
But it's still not clear to me, especially because of the code that is used by the author of the above mentioned tutorial. So, I will paste this code here and if you can give me explanations:
1. Here is the first .js file named pubsub.js, and I don't understand it:
(function($) {
var o = $({}); // ??? what is this ???
$.subscribe = function() { // ??? and this ???
o.on.apply(o, arguments); // ??? o.on.apply(o, arguments) ???
};
$.unsubscribe = function() { // ??? and this ???
o.off.apply(o, arguments); // ??
};
$.publish = function() { // ??? and this ???
o.trigger.apply(o, arguments); // ?? o.trigger.apply(o, arguments); ??
};
}(jQuery));
I know that with jQuery you can use $( document ).ready() or $(function() but I've never seen (function($) { ... }(jQuery)); - what does this mean/do? Also, I don't understand the rest of the code...
2. The next file is app.js and it contains:
(function() {
$.subscribe('form.submitted', function() {
$('.flash').fadeIn(500).delay(1000).fadeOut(500);
})
});
What does this actually do? Again, what (function() { ... }); means/do? And as for the rest of code, can you explain to me $.subscribe('form.submitted', function() {?
3. Finally, we have something like this:
$.publish('form.submitted', form); // publish?
This also is not clear to me.
I understand that all this is a basic implementation of PubSub Pattern with jQuery, but I still don't get why would someone do in this way (by using this pattern), I have read that answer on Stackoverflow, but it's still unclear to me... I guess that if I understand this code, then it would become clearer to me why and when to use this pattern.
In the case of (function($) { ... }(jQuery));, the author is passing the jQuery instance in as a parameter. Inside the function (which has it's own scope), the $ is a reference to the jQuery instance that was passed in.
"Pub Sub" is just another term for Event Management, or Event Handling. All you're saying is "When [this] happens, do [that]".
When you "subscribe", you are passing in 2 parameters, the "event" that you are listening for, and the code you want to run when the event "fires".
When you "publish", you are "firing" (or triggering) that event.
Think of it like the onclick event. When you set something up on the onclick event, you are subscribing to that event. When you click, you are publishing that event.
Related
I want to be able to put the code in one place and call it from several different events.
Currently I have a selector and an event:
$("input[type='checkbox']").on('click', function () {
// code works here //
});
I use the same code elsewhere in the file, however using a different selector.
$(".product_table").on('change', '.edit_quantity', function () {
// code works here //
});
I have tried following the advice given elsewhere on StackOverflow, to simply give my function a name and then call the named function but that is not working for me. The code simply does not run.
$(".product_table").on('change', '.edit_quantity', function () {
calculateTotals() {
// code does not work //
}
});
So, I tried putting the code into it's own function separate from the event and call it inside the event, and that is not working for me as well.
calculateTotals() {
// code does not work //
}
So what am I doing wrong ?
You could pass your function as a variable.
You want to add listeners for events after the DOM has loaded, JQuery helps with $(document).ready(fn); (ref).
To fix your code:
$(document).ready(function() {
$("input[type='checkbox']").on('click', calculateTotalsEvent)
$(".product_table").on('change', '.edit_quantity', calculateTotalsEvent)
});
function calculateTotalsEvent(evt) {
//do something
alert('fired');
}
Update:
Vince asked:
This worked for me - thank you, however one question: you say, "pass your function as a variable" ... I don't see where you are doing this. Can you explain ? tks. – Vince
Response:
In JavaScript you can assign functions to variables.
You probably do this all the time when doing:
function hello() {
//
}
You define window.hello.
You are adding to Global Namespace.
JavaScript window object
This generally leads to ambiguous JavaScript architecture/spaghetti code.
I organise with a Namespace Structure.
A small example of this would be:
app.js
var app = {
controllers: {}
};
You are defining window.app (just a json object) with a key of controllers with a value of an object.
something-ctlr.js
app.controllers.somethingCtlr.eventName = function(evt) {
//evt.preventDefault?
//check origin of evt? switch? throw if no evt? test using instanceof?
alert('hi');
}
You are defining a new key on the previously defined app.controllers.somethingCtlrcalled eventName.
You can invoke the function with ();.
app.controllers.somethingCtlr.eventName();
This will go to the key in the object, and then invoke it.
You can pass the function as a variable like so.
anotherFunction(app.controllers.somethingCtlr.eventName);
You can then invoke it in the function like so
function anotherFunction(someFn) { someFn();}
The javascript files would be structured like so:
+-html
+-stylesheets
+-javascript-+
+-app-+
+-app.js
+-controllers-+
+-something-ctlr.js
Invoke via chrome developer tools with:
app.controllers.somethingCtlr.eventName();
You can pass it as a variable like so:
$(document).ready(function() {
$('button').click(app.controllers.somethingCtlr.eventName);
});
JQuery (ref).
I hope this helps,
Rhys
It looks like you were on the right track but had some incorrect syntax. No need for { } when calling a function. This code should behave properly once you add code inside of the calculateTotals function.
$(".product_table").on('change', '.edit_quantity', function () {
calculateTotals();
});
$("input[type='checkbox']").on('click',function() {
calculateTotals();
});
function calculateTotals() {
//your code...
}
You could just condense it all into a single function. The onchange event works for both the check box and the text input (no need for a click handler). And jQuery allows you to add multiple selectors.
$('input[type=checkbox], .product_table .edit_quantity').on('change', function() {
console.log('do some calculation...');
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div class="product_table">
<input type="checkbox">
<input class="edit_quantity">
</div>
I posted a similar issue earlier, but it was flagged as a duplicate. However, this referenced article did not answer my question, so I'll try this again, this time using the solution of said article in my example.
The solution provided in this article creates the same issue I had before: when there is more than one element, I cannot call any of the public methods of the plugin.
Since no working example was provided, let's start with the code the article gave:
(function($){
$.fn.myPlugin = function(options) {
// support multiple elements
if (this.length > 1){
this.each(function() { $(this).myPlugin(options) });
return this;
}
// private variables
var pOne = '';
var pTwo = '';
// ...
// private methods
var foo = function() {
// do something ...
}
// ...
// public methods
this.initialize = function() {
// do something ...
return this;
};
this.bar = function() {
// do something ...
};
return this.initialize();
}
})(jQuery);
I LOVE the internal loop so that it's applied to each instance of the element, but I feel the repeated "return this" is redundant. I think if we removed every single one of them, this plugin would work exactly the same. But, for the sake of argument, I'm going to leave them in my working example.
As you can see in this jsfiddle example, it works fine when there is only one element. The public method runs fine.
However, if I were to comment the other 4 elements back in like here, it throws an error in the console: "undefined is not a function". This, of course, makes sense since I'm attempting to run the public method on a reference to all elements on not an individual element.
Well, then I use .eq(0) to run the method only on the first instance of the element here, but I get the exact same error in the console.
So, why isn't calling the public method on the individual element working? Is this a scoping issue?
Please advise. Thanks!
Ok, so I think I've answered my own question. The issue is that I'm not applying a jQuery plugin to a DOM element. I'm applying it to a jQuery element. So, if I were to apply the jQuery plugin to a jQuery element, referenced like $element or $('.element'), I can then run any public methods because the scope is the same. But, if I were to reference it in a different way, like say $parentelement.eq(0), I'm using a difference reference, one that did not get the plugin applied to it, so naturally, it would not have the defined method. I think I'm getting the concept right. Still a little shaky on this. Maybe someone else can explain it better.
Nevertheless, while the above code does technically work, public methods are not practical on a jQuery plugin. I suggest instead using a Custom Event to make the jQuery plugin do something. Like this:
(function($) {
$.fn.extend({
myTestPlugin: function() {
if (this.length > 1) {
this.each(function() { $(this).myTestPlugin(); });
}
this.done = function() {
$(this).html('Done!');
};
var alsoDone = function() {
$(this).html('Also done!');
};
this.html('Replace me!');
this.on('alsoDone', alsoDone);
}
});
})(jQuery);
Here is an example where I am using trigger to make the plugin do something on an individual element, which works, but the method still fails as expected.
I hope this helps other people with similar issues.
Hi fellow Meteor friends!
Please note: I am using Tom's router!
So I'm trying to only display my template when the mongo collection is ready but for some reason it does not work! :(
I first followed this post: LINK
So I have my publish functions in the server.js and I subscribe to these functions inside my router, so no Deps.autorun() involved here (btw: is this the right approach? Deps.autorun() did not work for me properly):
So I have something like:
'/myroute': function(bar) {
Meteor.subscribe("myCollection", bar, function() {
Session.set('stuffLoaded', true);
});
return 'stuffPage';
}
In the template, where the data loaded from "myCollection" is displayed, I will have something like this:
<template name="stuffPage">
{{#if stuffLoaded}}
<!-- Show the stuff from the collection -->
{{else}}
<p>loading!</p>
{{/if}}
</template>
For some reason "loading!" is never displayed.
Also, for a couple of milliseconds, the "old data" from the last time the same template was displayed (but with another "bar" value provided to the publish function --> different data) is displayed.
This of course is not good at all because for a couple of ms the user can see the old data and suddenly the new data appears.
To avoid this "flash" I want to display "loading!" until the new data is loaded but again: this does not work for me! :-(
What am I doing wrong?
Thx in advance for your help!
EDIT:
Ok so the problem with the answer in the first post provided by #user728291 is the following:
For some reason the router stuff get's called AFTER the Deps.autorun() ... what is wrong here? :( (please note: eventsLoaded == stuffLoaded.)
Where do you guys put your Deps.autorun() for the subscriptions or in other words: What's your code mockup for this?
I actually really think that my code mockup is just plain wrong. So how do you make different subscriptions based on the route (or in other words: based on the template which is currently shown)?
AND: Where do you put the Deps.autorun()? Inside the router.add() function? Or just inside of (Meteor.isClient)?
I think #user728291's answer is pretty spot on, I'd just add that Meteor.subscribe returns a handle that you can use to check readiness:
Keep a reference to the handle
Deps.autorun(function() {
stuffHandle = Meteor.subscribe(Session.get('bar'));
});
Then check it in your template:
{{#if stuffHandle.ready}}
...
{{/if}}
Template.barTemplate.helpers({stuffHandle: stuffHandle});
And control it via the session:
'/myroute': function(bar) {
Session.set('bar', bar);
return 'barTemplate';
}
Better to put the subscription in a Deps.autorun and use Session variable to pass arguments from the router. Also, make sure you are setting stuffLoaded to false before the subscribe runs. Otherwise it just keeps its old value.
'/myroute': function(bar) {
if ( ! Session.equals( "bar", bar ) ) {
Session.set( "stuffLoaded", false); //subscription needs to be run
Session.set( "bar", bar ); // this change will trigger Dep.autorun
}
return 'stuffPage';
}
Deps.autorun ( function (){
Meteor.subscribe("myCollection", Session.get( "bar" ), function() {
Session.set("stuffLoaded", true);
});
});
You might need some initial default values for the Session variables if you are not getting what you want on the first time the page loads.
First off, you may be missing the actual function name for the callback as demonstrated in this post.
Meteor.subscribe("myCollection", bar, function onComplete() {
Session.set('stuffLoaded', true);
});
Which seems to be great practice. I don't usually miss a beat using this method.
Secondly, I'm not sure subscriptions inside routes work well? I'd rather do the following:
'/myroute': function(bar) {
Session.set("myCollectionParam", bar)
return 'stuffPage';
}
So then the subsciption finally looks like this:
Meteor.subscribe("myCollection", Session.get("myCollectionParam"), function onComplete() {
Session.set('stuffLoaded', true);
});
OR (not sure which works correctly for you, depending on your publish function):
Meteor.subscribe("myCollection", {bar: Session.get("myCollectionParam")}, function onComplete() {
Session.set('stuffLoaded', true);
});
Good luck!
EDIT
Just mentioning something about the publish function:
While Session.get("myCollectionParam") could return null, you can ensure the behaviour a bit more by using the following publish method:
Meteor.publish("myCollection", function(myCollectionParam) {
check(myCollectionParam, String);
return MyCollection.find({_id: myCollectionParam});
});
I don't know if I'm saying this right, so I'll just ask by explaining with an example.
Let's say I've written a jQuery plugin with an onShowEdit callback.
I later use my plugin and add a bunch of other default functions/methods to the event:
$('.editable_module:not(.custom)').editable({
onShowEdit: function(el){
initRequired();
$(':radio, :checkbox', el).prettyCheckboxes();
initDatePickers();
initChosen();
initMaskedInputs();
$('.dynamic_box.tabs').dynamicBoxTabs();
$('.trigger_dynamic_box').triggerDynamicBox('true');
}
});
So now I have a basic/default element (.editable_module) that calls the plugin and has some methods/functions that are going to be used in all instances.
My question comes when I have a need to add something to this for a 'one time' kind of deal (I need to add some behavior to this callback/event but not something that is used normally). Is it possible to extend or add to this callback/event without overwriting it? I mean, I know I can go in and do this:
$('#new_selector').editable({
onShowEdit: function(el){
initRequired();
$(':radio, :checkbox', el).prettyCheckboxes();
initDatePickers();
initChosen();
initMaskedInputs();
$('.dynamic_box.tabs').dynamicBoxTabs();
$('.trigger_dynamic_box').triggerDynamicBox('true');
//ADD SOME NEW STUFF HERE
}
});
But is that really my only option?
Thanks in advance for any input/suggestions.
You could consider jQuery's own event system as follows: http://jsfiddle.net/VQqXM/1/. You can integrate this in your $.fn function pretty easily - just pass the appropriate function as property of the object instead of a function literal.
$("input").on("foo", function() {
alert(1);
});
// later
$("input").on("foo", function() {
alert(2);
});
// later
$("input").trigger("foo"); // alerts 1 and 2
You can simply use .on/.off to bind and unbind events, and trigger them all with .trigger. jQuery also supports namespacing of the event names to make sure you're not using an already used event.
You could use the new $.Callbacks() method
var $onShowEditCBObj = $.Callbacks();
function onShowEditHandler() {
$onShowEditCBObj.fire();
}
$('#new_selector').editable({
onShowEdit: onShowEditHandler
});
// add default event to callbacks obj
$onShowEditCBObj.add(function(){
initRequired();
$(':radio, :checkbox', el).prettyCheckboxes();
initDatePickers();
initChosen();
initMaskedInputs();
$('.dynamic_box.tabs').dynamicBoxTabs();
$('.trigger_dynamic_box').triggerDynamicBox('true');
});
// add a one time method to the callbacks obj
function oneTimeEvent () {
alert("worky");
$onShowEditCBObj.remove(oneTimeEvent);
}
$onShowEditCBObj.add(oneTimeEvent)
With this setup, you can change what callbacks will be fired without having to do anything extra to the editable plugin.
Edit: I didn't realize that you wrote the plugin. With that in mind, pimvdb's answer is more robust than requiring the developer to code a certain way.
If I understand the question correctly, the key word here is "factory".
jQuery is itself a factory but to get what you describe, you need your plugin also to be a factory within the factory. That requires the plugin to be written in a certain way.
Probably the easiest approach is to use jQuery's UI widget factory. Read about it here.
Defining a separate function for onShowEdit should work.
var myOnShowEdit = function(el, extra_fn) {
//standard functionality goes here
if (typeof extra_fn==='function') extra_fn(); //support for extra stuff
}
$('.editable_module:not(.custom)').editable({
onShowEdit: function(el) {
myOnShowEdit(el);
}
});
$('#new_selector').editable({
onShowEdit: function(el) {
myOnShowEdit(el, function(){console.log('hi');});
}
});
This will give you fair flexibility to add whatever functionality you need in addition to the standard stuff. Just be aware of how this may shift contexts.
I have an object defined using literal notation as follows (example code used). This is in an external script file.
if (RF == null) var RF = {};
RF.Example= {
onDoSomething: function () { alert('Original Definition');} ,
method1 : function(){ RF.Example.onDoSomething(); }
}
In my .aspx page I have the following ..
$(document).ready(function () {
RF.Example.onDoSomething = function(){ alert('New Definition'); };
RF.Example.method1();
});
When the page loads the document.ready is called but the alert('Original Definition'); is only ever shown. Can someone point me in the right direction. I basically want to redefine the onDoSomething function. Thanks, Ben.
Edit
Thanks for the comments, I can see that is working. Would it matter that method1 is actually calling another method that takes the onDoSomething() function as a callback parameter? e.g.
method1 : function(){
RF.Example2.callbackFunction(function() {RF.Example.onDoSomething();});
}
Your code as quoted should work (and does: http://jsbin.com/uguva4), so something other than what's in your question is causing this behavior. For instance, if you're using any kind of JavaScript compiler (like Closure) or minifier or something, the names may be being changed, which case you're adding a new onDoSomething when the old one has been renamed. Alternately, perhaps the alert is being triggered by something else, not what you think is triggering it. Or something else may have grabbed a reference to the old onDoSomething (elsewhere in the external script, perhaps) and be using it directly, like this: http://jsbin.com/uguva4/2.
Thanks for the response .. in the end the answer was unrelated to the code posted. Cheers for verifying I wasn't going bonkers.