Keep the JavaScript loading even on scrolling - javascript

I am building a chrome Extension which loads a javascript to place an image in front of tweets only with URLs. The code below achieves the desirable, However on scrolling the page sometimes the URLs arent marked.
Any idea on this?
linkslist=document.body.getElementsByClassName("js-display-url");
var i=0;
for (var index=0;index<linkslist.length;index++)
{
console.log(linkslist[index]);
arrayoflinks[i]=linkslist[index].getAttribute("data-expanded-url") ;
linkslist[i].innerHTML=linkslist[i].innerHTML+"<img src='"+chrome.extension.getURL("green.png")+"' alt='green'/>";
i++;
}

Related

Is there a better way to handle loading arrays of images?

I have groups of related images that I would like to be able to change (but position in the same div) by clicking on different radio buttons.
Currently I am using arrays to handle the html,
var marketingImages = [image1HTML, image2HTML, image3HTML, image4HTML];
var salaryImages = [image1HTML, image2HTML, image3HTML, image4HTML];
And when a relevant radio button is clicked, a function runs to clear the html in the div (of possible previous images), and load the new images using .append.
$(document).ready(function() {
$("#marketing, #salary").click(leed);
function leed() {
$("#portfolio-images").html("");
if ($("#marketing").is(':checked')) {
var portfolioArray = marketingImages;
} else if ($("#salary").is(':checked')) {
var portfolioArray = salaryImages;
}
for (var i=0; i<portfolioArray.length; i++) {
$("#portfolio-images").append(portfolioArray[i]);
}
...
}
It seems to work well, but being a noob though I have to wonder if there's a better way to handle this. Technically these images are just thumbnails (that can be clicked on to load larger Lightbox versions), but I'm unsure of how well that would "really" load for someone.
Does somebody know if there's a better way to handle loading groups of images? Thanks.

Read data from iframe with JavaScript

My problem is as follows:
I designed a homepage and I Have a index (www.abc.com) site and a site with news(www.abc.com/index.html).
I tried to bring my headlines of all the news automatically to my index site. Therefore I programmed a small javascript function and it works locally but it doesn't work when it goes online.
The way I'm doing this is:
Include an iframe (www.abc.com/index.html) in my index
iframe is not visible
Getting the structure of the iframe in my JS
Picking out the information I need for the index
Copy the data into my index
I know that I can't get data out from iframes which are not in my webspace, but this is in my webspace.
<iframe name="nf" id="newsframe" src="http://www.rossegger.at/news.html"
style="visibility:hidden"></iframe>
<table id="news_table"></table>
function load_news() {
var con = document.getElementById("news_table");
var frame = window.frames['nf'].document.getElementsByClassName('n');
if(frame.length != 0)
{
con.innerHTML += "<tr><h2 color=white>NEWS</h2></tr><hr>";
for(var i=0; i<frame.length; i++)
{
con.innerHTML += "<tr>"+frame[i].textContent+"</tr><hr>";
}
}
}
The problem is frame.length is always 0 (online)
offline the value has the right value.
Can anyone help me?
You can't due to sandbox limitations in the browser. You have to approach the problem from a different angel, try fetch the iframe site with javascript and show it in a div. Or set up a rss page for your news site and get the headlines from that source.

Automatically rotate through content

I have 7 graphs that are accessible to me through a web site. I want to develop my own web application that automatically cycles through each of these graphs, so I can display them on a huge monitor.
I want the functionality to be similar to an image carousel but it would be for web pages instead of images. What are my options? A jQuery plugin? AJAX and an iframe? Keep in mind that I want the data to be live while I display it.
You could use javascript, and a Frame with a simple timer to load it.
Nothing complex needed,
In the title frame set add this:
<script language="JavaScript">
var toShow;
var URL = new Array ('http://www.google.com','www.yahoo.com','www.bit.ly');
function setupTimer() {
toShow = 0;
loadNext();
var t=setTimeout("loadNext()", 3000);
}
function loadNext(){
parent.reportframe.location=URL[toShow];
toShow++;
if (toShow>3) toShow = 0;
}
</script>
<body onLoad="setupTimer()">
Then it will keep reloading the frames.
I just wrote this, did not test it, let me know if you need more help.
http://jsfiddle.net/5dazE/5/show
That's a basic slideshow. You can add or remove sites and then press play. It will rotate every 30 seconds. the code can be fond here: http://jsfiddle.net/5dazE/5
it could use more work, but I am in agreement with #nycynik. It is a great idea.

How do I abort image <img> load requests without using window.stop()

I have a very long page that dynamically loads images as users scroll through.
However, if a user quickly scrolls away from a certain part of the page, I don't want the images to continue loading in that now out-of-view part of the page.
There are lots of other requests happening on the page simultaneously apart from image loading, so a blunt window.stop() firing on the scroll event is not acceptable.
I have tried removing & clearing the img src attributes for images that are no longer in view, however, since the request was already started, the image continues to load.
Remember that the image src was filled in as the user briefly scrolled past that part of the page. Once past though, I couldn't get that image from stop loading without using window.stop(). Clearing src didn't work. (Chrome & FF)
Similar posts I found that get close, but don't seem to solve this problem:
Stop loading of images with javascript (lazyload)?
Javascript: Cancel/Stop Image Requests
How to cancel an image from loading
What you are trying to do is the wrong approach, as mentioned by nrabinowitz. You can't just "cancel" the loading process of an image (setting the src attribute to an empty string is not a good idea). In fact, even if you could, doing so would only make things worst, as your server would continually send data that would get cancelled, increasing it's load factor and slow it down. Also, consider this:
if your user scroll frenetically up and down the page, he/she will expect some loading delays.
having a timeout delay (ex: 200 ms) before starting to load a portion of the page is pretty acceptable, and how many times will one stop and jump after 200 ms interval on your page? Even it it happens, it comes back to point 1
how big are your images? Even a slow server can serve about a few tens of 3Kb thunbnails per second. If your site has bigger images, consider using low and hi resolution images with some components like lightBox
Often, computer problems are simply design problems.
** EDIT **
Here's an idea :
your page should display DIV containers with the width and height of the expected image size (use CSS to style). Inside of each DIV, add an link. For example :
<div class="img-wrapper thumbnail">
Loading...
</div>
Add this Javascript (untested, the idea is self describing)
$(function() {
var imgStack;
var loadTimeout;
$(window).scroll(function() {
imgStack = null;
if (loadTimeout) clearTimeout(loadTimeout);
loadTimeout = setTimeout(function() {
// get all links visible in the view port
// should be an array or jQuery object
imgStack = ...
loadNextImage();
}, 200); // 200 ms delay
});
function loadNextImage() {
if (imgStack && imgStack.length) {
var nextLink = $(imgStack.pop()); // get next image element
$('<img />').attr('src', nextLink.attr('href'))
.appendTo(nextLink.parent())
.load(function() {
loadNextImage();
});
// remove link from container (so we don't precess it twice)
nextLink.remove();
}
};
});
Well, my idea:
1) initiate an AJAX request for the image, if it succeeds, the image goes to the browser cache, and once you set the 'src' attribute, the image is shown from the cache
2) you can abort the XHR
I wrote a tiny server with express emulating the huge image download (it actually just waits 20 seconds, then returns an image). Then I have this in my HTML:
<!DOCTYPE html>
<html>
<head>
<style>
img {
width: 469px;
height: 428px;
background-color: #CCC;
border: 1px solid #999;
}
</style>
</head>
<body>
<img data-src="./img" src="" />
<br />
<a id="cancel" href="javascript:void(0)">CANCEL</a>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script>
$(function () {
var xhr, img = $('img'), src = img.data('src');
xhr = $.ajax(src, {
success: function (data) { img.attr('src', src) }
});
$('#cancel').click(function (){
xhr.abort();
})
});
</script>
</body>
</html>
You can load your images using ajax calls, and in case that the uses scrolls-out, you can abort the calls.
In jQuery pseudo-code it would be something like that (forgive me mistakes in syntax, it is just an example):
1) tag images that you want to load
$(".image").each( function(){
if ( is_in_visible_area(this) ) { // check [1] for example
$(this).addClass("load_me");
} else {
$(this).addClass("dont_load");
}
});
2) load images
ajax_requests = {};
$(".image.load_me").each( function(){
// load image
var a = $.ajax({
url: 'give_me_photos.php',
data: {img: photo_id},
success: function(html){
photo_by_id(photo_id), img.append(html);
}
});
ajax_requests[photo_id] = a;
});
3) cancel loading those out of the screen
for( id in ajax_requests ) {
if ( ! is_in_visible_area(id) ) {
ajax_requests[id].abort();
}
}
Of course, add also some checking if the image is already loaded (e.g. class "loaded")
[1]. Check if element is visible after scrolling
[2]. Abort Ajax requests using jQuery
BTW, another idea that might work:
1) create a new iframe
2) inside of the iframe have the script that starts loading the image, and once it's loaded, call the .parent's method
3) when in need, stop the iframe content loading using .stop on the iframe object
Use a stack to manage ajax requests (means you will have serial loading instead of parallel but it is worth it)
On scroll stop, wait for 300ms and then push all images inside view-area into stack
Every time a user scrolls check if a stack is running. (fyi - you can stop all requests to a particular url instead of killing all ajax calls. also you can use regex so it should not stop any other requests on the page)
If an existing stack is running - pop all the images that are in it except for the top most one.
On all ajax calls - bind beforeSend() event to remove that particular image from the stack
It is late right now, but we have done something very similar at work - if you need the detailed code let me know.
Cheers!
Maybe you could serve the image through a php script which would check a field in the the db (or better yet a memcached) that would indicate stop loading. the script would portion up the image into chunks and pause in between each chunk and check if the stop flag for the particular request is. If it is set you send the header with A 204 no content which as soon as the browser gets it will stop receiving.
This may be a bit over kill though.
The solution could be a webworker. a webworker can be terminated and with him the connection.
But there is a small problem that the webworker uses the limited connections of the browser so the application will be blocked.
Right now I'm working on a solution with serviceWorkers - they don't have a connection limit (I hope so)

delay images for display purposes not efficiency using javascript?

I have run into numerous sites that use a delay in loading images one after the other and am wondering how to do the same.
So i have a portfolio page with a number of images 3 rows of 4, what i want to happen is for the page to load,except for the images in img tags. Once the page has loaded i want images 1 of each row to load then say 0.5 seconds later the next image in the row(s) and so no. I'm going to have a loading gif in each image box prior to the actual image being displayed.
I know its doable but cant seem to find the term for doing this. This is purely for looks as it is a design site.
Thanks for the help.
This is very easy to do in jQuery
$('img').each(function(i) {
$(this).delay((i + 1) * 500).fadeIn();
});
Fiddle: http://jsfiddle.net/garreh/Svs7p/3
For fading in rows one after the other in a table it just means changing the selector slightly. Remember to change from div to img -- I just used div for testing
$('tr').each(function(i) {
$('td div', this).delay((i + 1) * 500).fadeIn();
});
Fiddle: http://jsfiddle.net/garreh/2Fg8S/
Here is what you can do, you can load the image tags with out the src and using a custom property:
<img alt='The image' path='image/path.jpg' />
then you can use javascript to load the images when the site is loaded or whenever you please;
// simplified
window.onload = function () {
var images = document.getElementsByTagName('img');
// loop and assign the correct
for (var i =0; i < images.length;i++){
var path = images[i].getAttribute('path');
images[i].src = path;
}
}
I hope you get the concept of how the images are delayed
**please note the path attribute is not a standard one.
The easiest way I can think to do this is to have a table set up that will eventually hold the image tags, but have none on load. Javascript can loop through an array of image urls, and insert those image tags into random locations on the table.
If you want to have the delay, setInterval is the perfect tool. http://www.w3schools.com/jsref/met_win_setinterval.asp
// You can hard-code your image url's here, or better still, write
// a server-side script that will read a directory and return them
// so it is fully dynamic and you can add images without changing code
unpickedImages = array();
// Start loading
loadAllImages = setInterval( insertImage, 600 );
function insertImage() {
if( unpickedImages.length > 0 ) {
var imageUrl = unpickedImages.shift();
// pick empty x, y on your table
// Insert the image tag im that <td></td>
} else {
clearInterval( loadAllImages );
}
}
You really don't need javascript to do this. If you specify the image sizes in the HTML or CSS, the browser will layout and display the page while loading the images, which will likely be loaded in parallel. It will then display them as soon as it can.
That way if users re-visit your site and have the images cached, they all show up immediately. If you have a script to load the images after a delay, you are making visitors wait for content unnecessarily and all their efforts to have a faster browser and pay for a fast internet connection has gone to waste.

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