Develop Reference

Javascript - passing a variable to event handler

Apologies if my problem sounds trivial to JS experts.
I've created an image slider (carousel) and, while loading thumbnails, I'm trying to create a reference to a full-size image, so that when a thumbnail is clicked - the image opens in another div.
The relevant code within window.onload handler is:
for (var i = 0; i < numImages; ++i) {
var image = images[i],
frame = document.createElement('div');
frame.className = 'pictureFrame';
/* some styling skipped */
carousel.insertBefore(frame, image);
frame.appendChild(image);
} /* for */
My first attempt was to add "onclick" at the end of the for loop:
frame.onclick= function () {
var largeImage = document.getElementById('largeImage');
largeImage.style.display = 'block';
largeImage.style.width=200+"px";
largeImage.style.height=200+"px";
var url=largeImage.getAttribute('src');
document.getElementById('slides').style.display = 'block';
document.getElementById("slides").innerHTML="<img src='url' />";
}
However, this may only work with hard-coded ids (e.g. 'largeImage').
Ideally, I need to pass image.src as a parameter but this (frame.onclick= function (image.src)) will not work.
My next thought was to put all logic of getting image.src to a separate function and displaying it with frame.onclick= myFunction;
However, I came over an example:
<input type="button" value="Click me" id="elem">
<script>
elem.onclick = function(event) {
// show event type, element and coordinates of the click
alert(event.type + " at " + event.currentTarget);
alert("Coordinates: " + event.clientX + ":" + event.clientY);
};
</script>
And here it is above me to understand why in this example a handler can accept a parameter.
What would be a correct way of assigning an image to the onclick event? Or is there a better way of turning a thumbnail into href?

While it might not be the best way, you could place the full size image path as a data-attribute on your thumbnail.
<img id="thumbnail" src="thumbnailpath" data-fullSizeImage="fullSizePath">
Then on your onclick, you could access the thumbnail element and get it's data- attribute.
function onClick(event){
var fullSizePath = event.currentTarget.getAttribute("data-fullSizeImage");
//Do whatever you want with fullsizepath
}
Code is untested; but, something like that should work based on my experience.
data attributes are a very flexible custom attribute for developers to use. Essentially you start with "data-" and then append a name to represent the attribute. Here is the documententation link.

You can create a closure (that is, an anonymous function) and register it as an event handler to access variables from outside the event handler inside the event handler itself:
for (var i = 0; i < numImages; ++i) {
/* create element */
element.addEventListener('click', function (event) {
console.log('The index is ' + i);
});
}
However, this will not quite work, since the variable i is changed every time the loop increases it, and closures don't "capture" the current value, only the reference itself, so at the end i will be equal to numImages for each event listener.
If you're using ES6 you can overcome this by using let (or const) to prevent this behavior:
for (let i = 0; i < numImages; ++i) {
/* create element */
element.addEventListener('click', function (event) {
console.log('The index is ' + i);
});
}
If using ES6 is not an option, you can still accomplish this in ES5 and earlier by wrapping the inside of your loop in a function that takes i as a parameter, which makes sure each event handler references different variables, since these parameters are different variables for each iteration:
for (var i = 0; i < numImages; ++i) {
(function (index) {
/* create element */
element.addEventListener('click', function (event) {
console.log('The index is ' + index);
});
})(i); /* pass in i here, which will be assigned to the index parameter */
}

Refresh a DIV content after faded it out

I got X DIV (TopRowRight1, TopRowRight2, TopRowRight3...) , each containing a different Google Geochart generated by a php page : GeochartPerProvince.php?template=X.
function getResult(template){
jQuery.post("GeochartPerProvince.php?template="+template,function( data ) {
jQuery("#TopRowRight"+template).html(data);
});
}
jQuery().ready(function(){
getResult(1);
setInterval("getResult(1)",10000);
getResult(2);
setInterval("getResult(2)",10000);
getResult(3);
setInterval("getResult(3)",10000);
});
jQuery(function () {
var $els = $('div[id^=TopRowRight]'),
i = 0,
len = $els.length;
$els.slice(1).hide();
setInterval(function () {
$els.eq(i).fadeOut(function () {
i = (i + 1) % len
$els.eq(i).fadeIn();
})
}, 5000)
});
Every 5 seconds, i fade out one and fade in the next one. This works perfectly.
For now, the php page in the DIV is refreshed every 10 seconds. This works too.
But what i dream about is that the php page in the DIV is reloaded AFTER the DIV is faded out instead of every 10 seconds. How to do it?
Solved. How it works properly:
function getResult(template){
jQuery.post("GeochartPerProvince.php?template="+template,function( data ) {
jQuery("#TopRowRight"+template).html(data);
});
}
$(document).ready(function(){
getResult(0);
getResult(1);
getResult(2);
//setInterval("getResult(2)",10000); <== keep this piece of code in case of need.
});
$(document).ready(function () {
var $els = $('div[id^=TopRowRight]'),
i = 0,
len = $els.length;
$els.slice(1).hide();
setInterval(function () {
$els.eq(i).fadeOut(function () {
i = (i + 1) % len
getResult(i);
$els.eq(i).fadeIn();
})
}, 10000)
});

You're already using a callback function after the element has been faded out. So why not call your getResult function inside it?
$el.fadeOut(function(){
// stuff
getResult(i)
})

I have a few suggestions and an example code for you to achieve what you need :
Use $ instead of jQuery for easier reading / writing
$(document).ready is the proper start point for dom related functions
If only one div is visible at a time, do not use too many divs. Most of the time one div is enough for alternating / refreshing content. If there is in/out animation or cross-fading, two divs would be needed. (Example below uses two divs)
Avoid using setInterval except you really really need. Logics with setTimeout better handles unexpected delays such $.post may cause.
start with html code something like this:
...
<div class="top-row-right" style="display:block"></div>
<div class="top-row-right" style="display:none"></div>
...
js:
$(document).ready( function() {
var len = 4; // 'I got X DIV..' This is where we put the value of X.
var template = -1;
function refreshChart() {
template = (template + 1) % len;
$.post("GeochartPerProvince.php?template="+template, function(data) {
var offscreenDiv = ('.top-row-right:hidden');
var onscreenDiv = ('.top-row-right:visible');
offScreenDiv.html(data);
onScreenDiv.fadeOut('slow', function() {
offScreenDiv.fadeIn();
setTimeout(refreshChart, 10000);
});
});
}
refreshChart();
});

Load content in div from a href tag in jQuery

I want to load all images before displaying them in a slideshow. I have been searching a lot but nothing seems to work. This is what i have so far and it doesn't work. I am loading images from the <a> tag from another div.
$('.slideshow').load(function(){
if (loaded<length){
first = $(settings.thumb).eq(loaded).find('a').attr("href");
$('<img src="'+first1+'"/>').appendTo('.slideshow');
}
else{ $('.slideshow').show(); }
loaded++;
});

Add an event listener to each image to respond to when the browser has finished loading the image, then append it to your slideshow.
var $images = $("#div_containing_images img");
var numImages = $images.length;
var numLoaded = 0;
var $slideshow = $(".slideshow");
$images.each(function() {
var $thisImg = $(this);
$thisImg.on("load", function() {
$thisImg.detach().appendTo($slideshow);
numLoaded++;
if (numLoaded == numImages) {
$slideshow.show();
}
});
});
It's a good idea to also listen for the error event as well, in case the image fails to load. That way you can increase numLoaded to account for broken image. Otherwise, your slideshow will never be shown in the event the image is broken.
Also note, that by calling detach() followed by appendTo() I am am moving the image in the DOM. If instead, you want to copy the image, use clone() instead of detach().
* EDIT TO MODIFY USER'S EXACT USE CASE *
var $images = $("li.one_photo a");
var numImages = $images.length;
var numLoaded = 0;
$images.each(function() {
$('<img />',
{ src: $(this).attr("href") })
.appendTo('.slideshow')
.on("load error", function() {
numLoaded++;
if(numLoaded == numImages) {
$('.slideshow').show();
}
});
});
* EDIT #2 *
Just realized you were putting everything in the $(".slideshow").load() function. Since $(".slideshow") represents a DIV, it will never raise a load event, and the corresponding function will never execute. Edited above accordingly.

Loading an image but onload/onerror not working as expected

I have a div
<div id='cards'>
Which I want to fill with images based on some logic. But only when images are first loaded into memory. Otherwise, through onerror I wanna fill in some text..
function pasteCard(card, to){
if (typeof(card) == 'string')
card = [card];
var image = [];
for (var i = 0; i < card.length; i++) {
image[i] = new Image();
image[i].src = '/sprites/open/' + card[i] + '.png';
image[i].onload = function() {
pasteImage(to, image[i]);
}
image[i].onerror = function() {
pasteText(to, card[i]);
}
// alert(card[i]) #1
}
function pasteImage(to, image) {
to.append(image);
}
function pasteText(to, text) {
// alert(card[i]) #2
to.append(text);
}
}
pasteCard(['ABC123', 'DEF456', 'GHI789'], $('#cards'));
But this isn't working.
Problem/weirdness: If only #2 alert is active it returns nothing. But strangely if #1 alert is also active it does kinda work... (but still doesn't load my images, and mostly fails too when other code is involved)
Question: Why is it not working without #1 alert (at least in that jsfiddle)
suggestions?: what should I do?

Onload and onerror events are fired (executed) outside the scope of your function so your variables will be undefined. In the event method you have access to this which is the image object. You can set a data attribute to each image and access that in your error event.
Here is an example:
http://jsfiddle.net/7CfEu/4/

The callbacks are not in the same scope as your image array is - therefor you need to declare a variable then will "connect the scopes" and use it inside the callbacks
also the i variable probably changes until the callback is fired - so by using it inside the callback you will get undefined behavior
for (var i = 0; i < card.length; i++) {
var current_card = card[i];
var current_image = new Image();
current_image.onload = function() {
pasteImage(to, current_image);
}
current_image.onerror = function() {
pasteText(to, current_card);
}
current_image.src = '/sprites/open/' + current_card + '.png';
image[i] = current_image;
}
Fiddle: http://jsfiddle.net/7CfEu/6/
(Also - closing the div tag is never a bad idea)

Just in case anyone ends up here for same reason I did.
Was going crazy because onload and onerror were not firing in the page I was building. Tried copy pasting
var myimage = new Image();
myimage.onload = function() { alert("Success"); };
myimage.onerror = function() { alert("Fail"); };
myimage.src = "mog.gif" //Doesn't exist.
Which was working within codepen and random otherwise blank pages.
Turns out the problem I was having was that I was doing AJAX requests earlier in the page. This involved authorization which in turn involved a call to
setRequestHeader();
This was resulting in a net::ERR_FILE_NOT_FOUND error instead of the expected GET mog.gif 404 (Not Found)
This seemed to prevent proper triggering of events.
Revert with
xhr.setRequestHeader("Authorization", "");

Jquery mega drop down loading after page loads

There may not be a fix for this. I am using a jquery drop down menu that loads when the DOM is ready. From what I understand this means it waits until the page is fully loaded until it becomes ready to be used.
This is problematic for a menu system because people want to use the menu right away often before the entire page is loaded.
Here is my site where you can see this happening.
http://bit.ly/g1sn5t
This is my script that I am using for the menu
$(document).ready(function() {
function megaHoverOver(){
$(this).find(".sub").stop().fadeTo('fast', 1).show();
//Calculate width of all ul's
(function($) {
jQuery.fn.calcSubWidth = function() {
rowWidth = 0;
//Calculate row
$(this).find("ul").each(function() {
rowWidth += $(this).width();
});
};
})(jQuery);
if ( $(this).find(".row").length > 0 ) { //If row exists...
var biggestRow = 0;
//Calculate each row
$(this).find(".row").each(function() {
$(this).calcSubWidth();
//Find biggest row
if(rowWidth > biggestRow) {
biggestRow = rowWidth;
}
});
//Set width
$(this).find(".sub").css({'width' :biggestRow});
$(this).find(".row:last").css({'margin':'0'});
} else { //If row does not exist...
$(this).calcSubWidth();
//Set Width
$(this).find(".sub").css({'width' : rowWidth});
}
}
function megaHoverOut(){
$(this).find(".sub").stop().fadeTo('fast', 0, function() {
$(this).hide();
});
}
var config = {
sensitivity: 2, // number = sensitivity threshold (must be 1 or higher)
interval: 0, // number = milliseconds for onMouseOver polling interval
over: megaHoverOver, // function = onMouseOver callback (REQUIRED)
timeout: 0, // number = milliseconds delay before onMouseOut
out: megaHoverOut // function = onMouseOut callback (REQUIRED)
};
$("ul#topnav li .sub").css({'opacity':'0'});
$("ul#topnav li").hoverIntent(config);
});
function clearText(field){
if (field.defaultValue == field.value) field.value = '';
else if (field.value == '') field.value = field.defaultValue;
}
// JavaScript Document
Is there anyway to get this to load before everything else?

You can put those scripts wherever you whant in the case of understanding exactly what you are doing.
HTML are rendered sequentially, so scripts cannot get the DOM object or js variables defined later in the document. That's why we usually use document onload event to do the init thing since all elements are loaded.
In this case, I guess you can probably put the scripts without document.ready right after the closing of ul#topnav tag.