Set onCLick callback inside object? - javascript

I have a carousel object, with images and a pager. The problem is I can't set the onClick to the pager. I'm obviously missing something here but I don't know what.
The error when I click in a pager item is:
Uncaught TypeError: Object #<HTMLDivElement> has no method 'scrollCarouselTo'
I set my onclick
carouselDots.on('click',function(){
this.scrollCarouselTo(1,5); // <-- problem lies here, how can i call this method?
});
and the scrollTo method
this.scrollCarouselTo=function(dotIndex, numDots)
{
//H_SCROLL.scrollToElement("#carouselItem"+dotIndex, 300);
H_SCROLL.scrollToPage(dotIndex, 0 , 300);
this.highlightCarouselDot(dotIndex, numDots);
}
Last, on my HTML file this is how I set it:
var tempCarousel = new Carousel();
tempCarousel.initialize(params,cont,scrollContainer);
My Carousel class: (parts of it that i think are relevant)
function Carousel() {
var container;
var pager;
var opt;
var thisCarousel;
//render the correct number of dots and highlight the indexed one
this.highlightCarouselDot=function(dotIndex, numDots)
{
var ui_str="";
console.log("numDots" + numDots);
for (var i=0;i<numDots;i++)
{
if (i==dotIndex)
ui_str+='<div class="carouselDot selected" id="carouselDot'+i+'"></div>';
else
ui_str+='<div class="carouselDot" id="carouselDot'+i+'"></div>';
}
console.log(ui_str);
console.log(pager);
pager.html(ui_str);
var carouselDots = $(pager.selector + " .carouselDot");
var dotSelected = $(pager.selector + " .selected");
carouselDots.css('background',opt.pagerImage);
carouselDots.width(opt.pagerSize);
carouselDots.height(opt.pagerSize);
carouselDots.on('click',function(){ //replace with touch
this.scrollCarouselTo(0,5);
});
dotSelected.css('background',opt.pagerSelectedImage);
}
this.scrollCarouselTo=function(dotIndex, numDots)
{
//H_SCROLL.scrollToElement("#carouselItem"+dotIndex, 300);
H_SCROLL.scrollToPage(dotIndex, 0 , 300);
this.highlightCarouselDot(dotIndex, numDots);
}
}
Thank you!

You are having trouble understanding where the scope is changing in your code. Yes this refers to the object you are in, but when you assign an event handler such as onclick, that function is run in the scope of the UI element that was clicked. This means that in your onclick code, this refers to the html object that was clicked, and not the highlightCarouselDot object.
One common solution to this problem is to use an extra variable to store the value of this.
var self = this;
at the start of your object, that way you can refer to self within your event handlers when you want to refer to the outside object.

Related

How to execute jquery when a variable with a CSS property changes

I need to set the scrollleft back to 0 on my wrapper when a specific css property changes. I'm a bit new to jquery and have never used variables, but I'm assuming that I'll need to declare the somewhat complex variable before the function, and then execute the function when the variable changes. Am I correct? It needs to continually respond like this to resize queries. This will be an epic solution for me if it works!
var changer = $(".dummy").css("float"); //whatever the float property is
$(document).ready(){
$(window).resize(function(){
if ($(".dummy").css("float") != changer ){
$(".wrapper").scrollLeft(0);
}
});
here is my suggestion: Use an ID for "dummy", if you have more than one "dummy" in your dom-tree you get an array with html elements from jquery.
$(document).ready(function() {
// First init for "dummy"
var $dummy = $("#dummy"),
dummyFloat = $dummy.css("float");
$(window).resize(function () {
var dynamicDummyFloat = $dummy.css("float");
if (dynamicDummyFloat != dummyFloat) {
$(".wrapper").scrollLeft(0);
dummyFloat = dynamicDummyFloat;
}
});
});
The code that you have written will work fine.

Accessing global variable and asynchronous issue

Below is some code I've just started to work on (an avatar generator experiment). I want to be able to click on a button and change the position of the canvas element, but I'm having troubles with some things.
In the click event function on the button I console.log out canvasTop ...
console.log(this.canvasTop);
... however, it gets undefined. I can access the variable anywhere else in the code except inside this click event function. Why is it like this?
The other thing is the next two lines ...
this.canvasTop += 10;
AvatarGenerator.canvas();
... on the first on these lines I want to iterate the canvasTop value, and on the second line call the function that draws the canvas. However, it seems like the second line runs before the first line (yes, JS is asynchronous I know) which means that the canvas element won't move until the next time I click the button. How can I solve this?
Thanks in advance!
The code:
AvatarGenerator = {
canvasTop: 50,
canvasLeft: 50,
canvas: $('#canvas')[0],
context: canvas.getContext('2d'),
init: function() {
AvatarGenerator.canvas();
AvatarGenerator.toolBox();
},
canvas: function() {
console.log(this.canvasTop); // <-- 50
this.context.beginPath();
this.context.moveTo(this.canvasLeft, this.canvasTop);
this.context.lineTo(300, 300);
this.context.stroke();
},
toolBox: function() {
var moveLeftBtn = $('#moveLeftBtn');
moveLeftBtn.on('click', function(){
console.log(this.canvasTop); // <-- undefined, why?
this.canvasTop += 10;
AvatarGenerator.canvas();
});
}
};
The click handler is called in a different context, so this doesn't point to your object anymore.
Try this:
var self = this;
moveLeftBtn.on('click', function(){
console.log(self.canvasTop);
self.canvasTop += 10;
AvatarGenerator.canvas();
});
Or, for modern browsers, you can bind your object to your function so you don't need self:
moveLeftBtn.on('click', function(){
console.log(this.canvasTop);
this.canvasTop += 10;
AvatarGenerator.canvas();
}.bind(this));
//^^^^^^^^^^ this determines what 'this' in the callback function is pointing to

How do i call a spcific jquery function form within another function?

I have the following code which is not working
jQuery
jQuery(window).bind("load", function() {
function effects(content_name,active_name)
{
// switch all tabs off
$(active_name).removeClass("active");
// switch this tab on
$(this).addClass("active");
// slide all content up
$(content_name).slideUp();
// slide this content up
var content_show = $(this).attr("title");
$("#"+content_show).slideDown();
}
$("a.tab_1").click(function () {
var content_name = '.content_a';
var active_name = 'a.tab_1.active';
effects(content_name,active_name);
});
$("a.tab_2").click(function () {
var content_name = '.content_b';
var active_name = 'a.tab_2.active';
effects(content_name,active_name);
});
$("a.tab_3").click(function () {
var content_name = '.content_c';
var active_name = 'a.tab_3.active';
effects(content_name,active_name);//create effects with the content
});
});
Its a set of tab groups upto 8 in number. Writing individual functions will have an adverse effect on loading time.
Answer 2 hours later:
Thank you all for pointing out the "effetcs" mistake in the code.
The other mistake was I was doing was not passing "$(this)" as a parameter into the called function "effects".
I Have adjoined the link where the necessary changes are done and the code works.
[jsfiddle] http://jsfiddle.net/phyGS/2/
Replace effetcs with effects at the first block, and replace every occurrence of
effects(content_name,active_name);
with
effects.call(this, content_name, active_name);
This call method assigns a new value to the this property of function effects.

How to pass an array to an user defined object or convert non-OO code to OO? javascript

I really have trouble with OO coding in js. I have written a piece of code which rotates through 3 divs, and pauses on hover of any div. This code is just regular js using an array/json as the input. the code is a bit long so sorry about that. I just need some guidance on how I can convert this primitive code to a better form, as in OO and encap. When I tried myself I could not pass the slides array/json to my defined object. Is there a trick or guideline i can follow on how to rewrite this to a better form?
Edit - What is a good guideline to follow so I can rewrite this with objects instead of global variables and loose functions
var slideIndex = 0;
var prevIndex = 0;
var t;
function initPromo(){
sortSlides();
nextPromo();
addListeners();
}
function addListeners(){
for(var i=0; i<slides.length; i++)
$(slides[i].el).hover(function(){ stopPromo(); }, function(){ resumePromo(); });
}
function resumePromo(){ startTimer(); }
function stopPromo(){ clearTimeout(t); }
function nextPromo(){
if(slideIndex > 0 || prevIndex > 0) $(slides[prevIndex].el).css("display","none");
$(slides[slideIndex].el).css("display","block");
prevIndex = slideIndex;
slideIndex = (slideIndex<slides.length-1) ? slideIndex+1 : 0;
startTimer();
}
function startTimer(){ t = setTimeout("nextPromo()", 3000); }
function SortByWeight(a,b) { return b.weight - a.weight; }
function SortByWeightFr(a,b) { return b.frWeight - a.frWeight; }
function sortSlides(){
($("body.en").length > 0) ? slides.sort(SortByWeight) : slides.sort(SortByWeightFr);
}
var slides = [
{
el:'#ps1',
weight:1,
frWeight:3
},
{
el:'#ps2',
weight:0.5,
frWeight:6
},
{
el:'#ps3',
weight:4,
frWeight:9
}
];
window.onload = function () {
initPromo();
};
HTML
<body class="en">
<div id="homepageSlides">
<div id="promoSlides">
<div id="ps1">ps1</div><div id="ps2">ps2</div><div id="ps3">ps3</div>
</div>
</div>
</body>
Edit: Early days in OO coding, not asked in the right way
Well your "plain javascript" code is already taking you part way there. The first function you have defined identies the domain object: Promo.
var Promo = function () { };
You have actions on an instance of promo, init, start, stop, resume, etc. These can be defined on the prototype of Promo.
Promo.prototype.init = function() {
// ...
};
It could get a little annoying typing prototype each time, so we could bundle the prototype into a pointer that allows us a lot easier access...
var Promo = function () { };
(function(obj) {
obj.init = function() {
// ...
};
})(Promo.prototype);
So we've got some structure but we need to now separate concerns. Throughout your plain javascript you've got config type data strewn through the code. It's generally a good idea to isolate these bits of data to a single entry point for your object.
obj.init = function(_el) {
// where _el is the base element of this widget
};
I see you're also using jQuery which is good because it gives you a lot of power. One convention I like to use is instead of passing a huge amount of config data into a given widget, I like to give my objects minimal config and let them inspect the HTML to determine additional configuration data. This has the added advantage of if you wanted to add slides in the future or otherwise make changes to the slide content you need'nt worry about changing the JS.
Let's say we were to alter the slide HTML to look like...
<div id="promoSlides">
<div data-type="slide" data-slide-id="1">ps1</div>
<div data-type="slide" data-slide-id="2">ps2</div>
<div data-type="slide" data-slide-id="3">ps3</div>
</div>
Using jQuery we could identify how many slides are present.
obj.init = function(_el) {
this.baseElement = $(_el);
this.slides = this.baseElement.find('*[data-type="slide"]');
};
Now we're passing in minimal config, we've separated out the identification of the slides to the HTML, and we've got a nice pattern for a self-sufficient object. The rest would be to fill in the details (totally untested, but something like this)...
var Promo = function () { };
(function (obj) {
obj.init = function(_el, _delay) {
// Initialize markup
this.baseElement = $(_el);
this.slides = this.baseElement.find('*[data-type="slide"]');
this.slideDelay = _delay;
// Sort slides
// (not sure what's going on here)
// Bind events
this.baseElement
.on('mouseenter', this.stop.bind(this))
.on('mouseleave', this.start.bind(this));
};
obj.start = function() {
this.timer = setInterval(this.advance.bind(this), this.slideDelay);
};
obj.stop = function() {
clearInterval(this.timer);
};
obj.advance = function() {
// Slide the visible slide off screen
// (note: the parent tag will need overflow:hidden)
var visible = this.baseElement.find('*[data-type="slide"]:visible');
visible.animate({ left: '-' + (visible.width()) + 'px' }, 1000);
// Slide the next slide in
var next = visible.next();
next.css('left', this.baseElement.width() + 1).animate({ left: '0' }, 1000);
};
})(Promo.prototype);
Note that I made use of bind which isn't supported yet in older versions of IE.
Its not the converting to object oriented style what is needed for that code there.
Here are issues i see there:
pollution of global scope
mixing fixed CSS rules with Javascript
use of .length attribute within a loop
no event delegation
misplacement of <script> tag, resulting in use of window.onload
creating new jQuery object when it is not needed
use of CSS3 selectors in jQuery calls
no clue how to use setTimeout()
tight coupling to HTML ( id on each slide )

JS Class and overriding the JQuery event handlers

This should be simple, but for reason I can't quite fathom it doesn't work and - more importantly - I can't find the right question to ask of Google!
What I want to do is prototype an event binder for a JS class as per below, what actually happens is nothing, unless I call .bind() directly on the box object.
function Box()
{
this.Width = 200;
this.Height = 200;
this.WrapperClass = "boxWrapper";
this.TitleClass = "boxTitle";
this.ContentClass = "boxContents";
this.Title = "This is a box";
this.Content = "This is some box contents";
}
Box.prototype.Html = function()
{
var box = $('<div></div>').addClass(this.WrapperClass);
box.append($("<div></div>").addClass(this.TitleClass).append(this.Title));
box.append($("<div></div>").addClass(this.ContentClass).append(this.Content));
box.width(this.Width);
box.height(this.Height);
return box.outerHTML();
}
Box.prototype.Bind = function(event, eventDelegate)
{
this.bind(event, eventDelegate);
}
function clickDelegate(message)
{
alert(message);
}
$(document.ready(function() {
var box = $(new Box().Html());
box.Bind('click', clickDelegate('text'));
$('body').append(box);
}
You have to append box before binding events.
I have created a little fiddle starting with your code and debugging it.
FYI : jQuery object has no method outerHTML, So I've embedded the newly created div in one other.
I've made several changes to your code that's why I'm not posting it here.

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