Develop Reference

JQuery - how to get the app object from a button click function

In my javascript file, I have defined an app object that takes an initialization function which is triggered upon document ready via JQuery.
$(document).ready(function() {
console.log("JQuery ready");
app.initialize();
});
The app is defined as
var app = {
_GPS_ENABLED: false,
initialize: function() {
var self = this;
// deviceready Event Handler
$(document).on('deviceready', function() {
... ...
// BIND A CLICK EVENT TO A FUNCTION DEFINED IN A LATER STEP
$('#isGPSenabled').on("click", self.isGPSenabled);
... ...
});
},
isGPSenabled: function() {
cordova.plugins.diagnostic.isGpsLocationEnabled(function(enabled) {
// HERE I NEED TO ACCESS THE "APP" ATTRIBUTE "_GPS_ENABLED"
._GPS_ENABLED = enabled; // HOW CAN I ACCESS THE _GPS_ENABLED ATTRIBUTE ON APP
});
}
}
The HTML part has:
<button id = "isGPSenabled">IS GPS ENABLED</button>
How can I access the app's attribute from the function attached to a button?

Previously I've referenced the object by it's name within itself. I think it was a pattern I saw once which worked for my needs at the time. Haven't really thought about the positives or negatives much but it has never caused me any issues in previous work.
Here is an example to to demonstrate:
const app = {
isEnabled: null,
init: () => {
app.isEnabled = false;
},
toggleEnabled: () => {
app.isEnabled = !app.isEnabled;
},
displayEnabled: () => {
console.log('isEnabled?:', app.isEnabled);
}
}
app.displayEnabled(); // null
app.init();
app.displayEnabled(); // false
app.toggleEnabled();
app.displayEnabled(); // true

object oriented jquery - event handlers not working

I am moving some jquery functions into a javascript object to clean up some code. My problem is, when I put methods on my object's constructor, my event handlers don't seem to respond to events but respond fine if my handlers are helper methods and are outside of the object's constructor.
Here's my code that isn't working
function MyConstructor() {
this.init();
this.selectAllHandler();
}
MyConstructor.prototype = {
init: function() {
$(document).on('click', '#my_element', this.selectAllHandler);
},
selectAllHandler: function() {
// some code in here
}
}
When using this, my code does not error out and putting console.log's atop the function runs. But when I try to click on the thing to trigger the handler, it doesn't do anything.
But, if I build it as a constructor using a method outside of the object, it works fine. Like this
function MyConstructor() {
this.init();
}
MyConstructor.prototype = {
init: function() {
$(document).on('click', '#my_element', selectAllHandler);
}
}
function selectAllHandler() {
// code that works fine
}
what am I doing wrong that I cannot call the handlers inside the object's prototype?
edit
Here is my new code. The problem now, is $(this) seems to refer to the constructor and no longer refers to the element being clicked on.
function MyConstructor() {
this.init();
}
MyConstructor.prototype = {
init: function() {
$(document).on('click', '#my_element', this.selectAllHandler.bind(this));
},
selectAllHandler: function() {
var checkboxes = $('.prospect_select_box');
console.log($(this)); // => [MyConstructor]
if (!$(this).prop('checked')) {
console.log('here')
checkboxes.prop('checked', false);
$('#prospect-left-section').hide();
} else {
console.log('other here')
checkboxes.prop('checked', true);
$('#prospect-left-section').show();
}
}
}

You have two objects you are interested in: the constructed object, and the clicked element. The first you need to find the method selectAllHandler, the second to work with $(this) within that function. Obviously both of them cannot be this at the same time, so you'll need to reference one of them in a different way.
Here is how you could do that.
function MyConstructor() {
this.init();
}
MyConstructor.prototype = {
init: function() {
var that = this;
$(document).on('click', '#my_element', function () {
that.selectAllHandler.call(this);
});
},
selectAllHandler: function() {
$(this).text('clicked!');
}
}
new MyConstructor();
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="my_element">click me</button>
Note how call is used to make sure the selectAllHandler will run with this set to what jQuery passed on as element.
If however, you need to also reference the constructed object with this inside setAllHandler, then do it the other way around, and use that as this, but reference the clicked element via the event object that is passed to the function:
function MyConstructor() {
this.init();
}
MyConstructor.prototype = {
init: function() {
var that = this;
$(document).on('click', '#my_element', this.selectAllHandler.bind(this));
},
selectAllHandler: function(e) {
var elem = e.target;
$(elem).text('clicked ' + this.other);
},
other: 'me!'
}
new MyConstructor();
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="my_element">click me</button>

JavaScript: using THIS inside object function and binding event

I have an Object and I want to bind a function to a button when Object was initialized.
var MyClass = {
Click: function() {
var a = MyClass; // <---------------------- look here
a.Start();
},
Bind: function() {
var a = document.getElementById('MyButton');
a.addEventListener('click', this.Click, false); //<---------- and here
},
Init: function() {
this.Bind();
}
}
So, I'm new at using it and I don't know if object can be declared like this (inside Click() function that should be done after clicking a button):
Is it a bad practise? Which could be the best way in this case when adding an event here?
Edit: fiddle

Firstly you have a syntax error. getElementsById() should be getElementById() - no s. Once you fix that, what you have will work, however note that it's not really a class but an object.
If you did want to create this as a class to maintain scope of the contained methods and variables, and also create new instances, you can do it like this:
var MyClass = function() {
var _this = this;
_this.click = function() {
_this.start();
};
_this.start = function() {
console.log('Start...');
}
_this.bind = function() {
var a = document.getElementById('MyButton');
a.addEventListener('click', this.click, false);
};
_this.init = function() {
_this.bind();
};
return _this;
}
new MyClass().init();
<button id="MyButton">Click me</button>

For event listeners it's easiest and best to use jQuery, for example if you want to have some .js code executed when user clicks on a button, you could use:
https://api.jquery.com/click/
I don't know how new you are to .js, but you should look up to codecademy tutorials on JavaScript and jQuery.
.click() demo:
https://www.w3schools.com/jquery/tryit.asp?filename=tryjquery_event_click

Calling jQuery plugin public function within plugin

I know, there are quite a few examples on the Web, but finding real one out of them all is tough for beginner. So I want to create jQuery plugin with public methods. Example code:
(function($) {
$.fn.peel = function(options) {
var defaults = {
};
var settings = $.extend({},defaults, options);
this.public = function() {
alert("public");
};
var private = function() {
alert("private");
}
return this.each(function() {
//this.public();
private();
});
};
})(jQuery);
As I found, this is the way to make public function, which could be called like this :
var peel = $('img').peel();
peel.public();
So far it works as expected - public() can be called. But what if i want to call that function within my plugin? I commented out in this.each() because it does not work. How can i achieve that?

One way to create publicly accessible methods within your plugins is to use the jQuery UI widget factory. This is the framework that jQuery UI uses for all of it's supported UI widgets. A quick example would look like this:
(function( $ ) {
$.widget( "something.mywidget", {
// Set up the widget
_create: function() {
},
publicFunction: function(){
//...
}
});
}( jQuery ) );
var $w = $('#someelement').mywidget();
$w.mywidget('publicFunction');

Creating custom jQuery function without selector prerequisite

I know that I can create custom jQuery plugins by using the $.fn.myFunction constructor, and the calling the custom function in JavaScript as $('selector').myFunction().
However, for a project I'm currently working on, I need to be able to define a function that does not require a selector to work.This is actually for a MessageBox plugin, which will act in a similar manner to C#'s MessageBox class. As such, I would ideally like to create the function as MessageBox, and then call it as follows:
var myMessage = $.MessageBox(); and then in turn myMessage.Show();
Notice the lack of selector brakets in the jQuery reference at the beginning of the function call.
Any advice on the best practice for this would be gratefully received.

This should work:
jQuery.MessageBox = function() {
var show = function() {
// something...
}
var hide = function() {
// something...
}
return {
show: show,
hide: hide
}
}

relipse has a good point - as you are cluttering the main namespace. A solution if you have more objects than just eg. MessageBox is to create your own namespace like this:
jQuery.myLib = {
MessageBox: function() {
var show = function() {
// something...
}
var hide = function() {
// something...
}
return {
show: show,
hide: hide
}
}
}
That means you are only taking one place in the main namespace (the name of your library, in this case myLib). You'd call it like this:
jQuery.myLib.MessageBox.show()

(function ($) {
$.MessageBox = function () {
var show = function () {
// something...
}
var hide = function () {
// something...
}
return {
show: show,
hide: hide
}
}
})(Jquery);
I think you better scope to Immediate invocation function to avoid collision with namespaces.