Javascript/JQuery Execute Javascript Only On Page Focus - javascript

Is it possible in javascript to only execute javascript if the user is on the actual tab/page?
Like if he switches to another tab then the javascript process will be paused and when he returns to the tab the javascript will continue the process.

There is no direct way unless you use browser-specific code, or code that's not completely standard (see katspaugh's answer).
'Stop' solution
design your code so that it is "stoppable". That's something you have to figure out for your context.
Then add something like below:
..
<html>
<head>
</head>
<body>
<script>
window.onblur = function() {
yourStopFunctionHere().
}
</script>
</body>
</html>
'Assert' solution
Insert the following code where it really matters that the window has focus:
if(windowHasFocus()) {
//your code here
}
There are different methods for testing if window has focus: JavaScript / jQuery: Test if window has focus
Asyncronous solution
whenWindowHasFocus(fn); //where fn is the function you want to only run when window has focus
One of two possible implementations exist.....
Waiting via setTimeout
function WhenWindowHasFocus(yourFunction){
if(windowHasFocus()) {
yourFunction();
}
setTimeout(function(){ WhenWindowHasFocus(yourFunction); }, 1000);
}
Waiting via custom events
Or even better, if you can wrap the window-focused-dependent functionality (the functionality dependent on the window having focus) into a separate function, then "hook" that function to window.onfocus. Be careful with this one though. You don't wan't to completely overwrite the window.onfocus function (or you undo the previous work you just did). Instead, you may have to use custom events of some sort. Most js frameworks provide custom events. If you go this route, the window.onfocus function will simply trigger some custom event, and you don't have to manually writing any looping code with setTimeout.
//The below is pseudo-code. custom events differ between js frameworks
window.onfocus = function(){
window.FocusEvent.trigger()
}
function WhenWindowHasFocus(yourFunction){
if(windowHasFocus()) {
yourFunction();
}
window.focusEvent.addOnlyOnce(yourFunction);
}

Related

What is the working and requirement of this code in a webpage?

I downloaded a theme for a webpage. I found this piece of code in < head > of the index. I want to know what this script does and what if I remove it.
<meta name="keywords" content="Some Text"/>
<script type="application/x-javascript"> addEventListener("load", function() { setTimeout(hideURLbar, 0); }, false); function hideURLbar(){ window.scrollTo(0,1); } </script>
Thanks.
It looks like a pretty meaningless piece of code. Here is what it does in detail
addEventListener("load", function() {
setTimeout(hideURLbar, 0);
}, false);
Adds a new event listener. It is a piece of code waiting for a "trigger" or a condition (this being an event in this case) and it does something when that trigger is fired (condition is met). Since the target of the event is not specified, it's the window object it's would be attached to and since it's the load event it waits for here, this means it would wait until the entire page and all resources (e.g., images, scripts, CSS) belonging to it are completely loaded and rendered.
When that happens it would call setTimeout in order to schedule that the function hideURLbar is started after 0 milliseconds. Yes, that's like saying "execute it now" but this particular technique is a way to deal with old versions of Internet Explorer as sometimes the threading there could be overwhelmed and using setTimeout with a 0 parameter actually helps keep things managed.
function hideURLbar(){
window.scrollTo(0,1);
}
And this is what the actual hiteURLbar function is: it scrolls the page 1 pixel down from the top. Unless there is some other JavaScript that is triggered by this, it seems pretty useless.

How to execute code before window.load and after DOM has been loaded?

Here is the circumstance:
I have 2 pages:
1 x html page
1 x external Javascript
Now in the html page, there will be internal Javascript coding to allow the placement of the window.onload, and other page specific methods/functions.
But, in the external Javascript I want certain things to be done before the window.onload event is triggered. This is to allow customized components to be initialized first.
Is there a way to ensure initialization to occur in the external Javascript before the window.onload event is triggered?
The reason I have asked this, is to attempt to make reusable code (build once - use all over), to which the external script must check that it is in 'order/check' before the Javascript in the main html/jsp/asp/PHP page takes over. And also I am not looking for a solution in jQuery #_#
Here are some of the links on Stack Overflow I have browsed through for a solution:
Javascript - How to detect if document has loaded (IE 7/Firefox 3)
How to check if page has FULLY loaded(scripts and all)?
Execute Javascript When Page Has Fully Loaded
Can someone help or direct me to a solution, your help will be muchness of greatness appreciated.
[updated response - 19 November 2012]
Hi all, thanks for you advice and suggested solutions, they have all been useful in the search and testing for a viable solution.
Though I feel that I am not 100% satisfied with my own results, I know your advice and help has moved me closer to a solution, and may indeed aid others in a similar situation.
Here is what I have come up with:
test_page.html
<html>
<head>
<title></title>
<script type="text/javascript" src="loader.js"></script>
<script type="text/javascript" src="test_script_1.js"></script>
<script type="text/javascript" src="test_script_2.js"></script>
<script type="text/javascript">
window.onload = function() {
document.getElementById("div_1").innerHTML = "window.onload complete!";
}
</script>
<style type="text/css">
div {
border:thin solid #000000;
width:500px;
}
</head>
<body>
<div id="div_1"></div>
<br/><br/>
<div id="div_2"></div>
<br/><br/>
<div id="div_3"></div>
</body>
</html>
loader.js
var Loader = {
methods_arr : [],
init_Loader : new function() {
document.onreadystatechange = function(e) {
if (document.readyState == "complete") {
for (var i = 0; i < Loader.methods_arr.length; i++) {
Loader.method_arr[i]();
}
}
}
},
load : function(method) {
Loader.methods_arr.push(method);
}
}
test_script_1.js
Loader.load(function(){initTestScript1();});
function initTestScript1() {
document.getElementById("div_1").innerHTML = "Test Script 1 Initialized!";
}
test_script_2.js
Loader.load(function(){initTestScript2();});
function initTestScript2() {
document.getElementById("div_2").innerHTML = "Test Script 2 Initialized!";
}
This will ensure that scripts are invoked before invocation of the window.onload event handler, but also ensuring that the document is rendered first.
What do you think of this possible solution?
Thanking you all again for the aid and help :D
Basically, you're looking for this:
document.onreadystatechange = function(e)
{
if (document.readyState === 'complete')
{
//dom is ready, window.onload fires later
}
};
window.onload = function(e)
{
//document.readyState will be complete, it's one of the requirements for the window.onload event to be fired
//do stuff for when everything is loaded
};
see MDN for more details.
Do keep in mind that the DOM might be loaded here, but that doesn't mean that the external js file has been loaded, so you might not have access to all the functions/objects that are defined in that script. If you want to check for that, you'll have to use window.onload, to ensure that all external resources have been loaded, too.
So, basically, in your external script, you'll be needing 2 event handlers: one for the readystatechange, which does what you need to be done on DOMready, and a window.onload, which will, by definition, be fired after the document is ready. (this checks if the page is fully loaded).
Just so you know, in IE<9 window.onload causes a memory leak (because the DOM and the JScript engine are two separate entities, the window object never gets unloaded fully, and the listener isn't GC'ed). There is a way to fix this, which I've posted here, it's quite verbose, though, but just so you know...
If you want something to be done right away without waiting for any event then you can just do it in the JavaScript - you don't have to do anything for your code to run right away, just don't do anything that would make your code wait. So it's actually easier than waiting for events.
For example if you have this HTML:
<div id=one></div>
<script src="your-script.js"></script>
<div id=two></div>
then whatever code is in your-script.js will be run after the div with id=one but before the div with id=two is parsed. Just don't register event callbacks but do what you need right away in your JavaScript.
javascript runs from top to bottom. this means.. if you include your external javascript before your internal javascript it would simply run before the internal javascript runs.
It is also possible to use the DOMContentLoaded event of the Window interface.
addEventListener("DOMContentLoaded", function() {
// Your code goes here
});
The above code is actually adding the event listener to the window object, though it's not qualified as window.addEventListener because the window object is also the global scope of JavaScript code in webpages.
DOMContentLoaded happens before load, when images and other parts of the webpage aren't still fully loaded. However, all the elements added to the DOM within the initial call stack are guaranteed to be already added to their parents prior to this event.
You can find the official documentation here.

Click button on load event

I have the following javascript -
function onLoad() {
if (!(document.applets && document.VLVChart && document.VLVChart.isActive())) {
setTimeout('onLoad()', 200);
return;
}
objChart = document.VLVChart;
PollEvent();
}
function fan() {
objChart.reorganize();
}
And then when the HTML page is loaded -
<body onLoad="onLoad()">
and have a button within the HTML that execute the fan() function -
<input type='button' value='Fan' onClick='fan();'>
Is it possible for me to activate the fan() function within the onload event so that a user does ont have to click the button?
EDIT
After trying the provided answers, on debugging the code breaks on the line -
objChart.reorganize();
Within the fan() function with the error -
SCRIPT5007: Unable to get value of the property 'reorganize': object is null or undefined
This is odd as when I manually click the button on the page, the function works fine.
Solution
After much head scratching I have realised that I was trying to load the fan() function before the page (and more specifically the objChart) had fully loaded. Hence why adding the function in the onLoad event was not working. I added a setTimeout -
function Fan()
{
setTimeout(function(){objChart.reorganize();},3000);
}
<body onload='onLoad(); fan();'>...
However inline JS is best avoided and you would do well to begin looking into centralised event management. There are various advantages to this.
An answer I wrote yesterday to another question outlines why this is. Something like jQuery makes this trivial if it's new for you.
$(function() {
$('body').on('load', function() {
onLoad();
fan();
});
});
Reading your question I assume you didn't even have tried. Just call that function from within your onLoad()-function:
function onLoad()
{
fan();
/* … */
}
Yes.
You can use <body onload='onLoad(); fan();'> as Utkanos suggests.
If you use jQuery, you can also stick a script in the head containing:
$(function(){
...
});
The jQuery function actually fires earlier, as is explained here.

jQuery document.ready vs pageLoad

I've picked up an existing project from another developer and ive noticed in the code that they are executing js code within three different event handlers...
function pageLoad() {
//execute code
}
$(document).ready(function() {
//execute code
});
$(function() {
//execute code
});
My question is - arent they all exactly the same? Or at least the last two? I understand that pageLoad is called by the .NET framework so it's not dependent on the jQuery library having loaded like the second two are - that's my understanding anyway - is that about correct?
$(document).ready()
Ideal for one time initialization.
Optimization black magic; may run slightly earlier than pageLoad().
Does not re-attach functionality to elements affected by partial postbacks.
pageLoad()
Unsuitable for one time initialization if used with UpdatePanels.
Slightly less optimized in some browsers, but consistent.
Perfect for re-attaching functionality to elements within UpdatePanels.
pageLoad and the jQuery ready handler are both methods of accomplishing similar things.
The second two examples are identical.
http://encosia.com/document-ready-and-pageload-are-not-the-same/
The last one is just a shorthand notation of the one above it. http://www.jquery4u.com/dom-modification/types-document-ready/
$(document).ready(function() {
`enter code here`
//execute code
});
$(function() {
`enter code here`
});
Both functions perform task in the same way, executes code inside them once the document is ready.
function pageLoad() {
`enter code here`
}
This executes after every post back, generally used with update panels controls as the above two functions does not execute every time or every post back.
$(document).ready() will not fire for the partial postbacks (happened from AJAX). In that case, you should use MS AJAX pageLoad function when you need to execute something when the page loads either from the full postback or partial.
The article given in the Encosia site is a good read.
In this site you will find the difference :)
Document.ready Vs pageLoad

JavaScript TinyMCE/jQuery race condition on firefox

I have a website with a form that uses TinyMCE; independently, I use jQuery. When I load the form from staging server on Firefox 3 (MacOS X, Linux), TinyMCE doesn't finish loading. There is an error in Firefox console, saying that t.getBody() returned null. t.getBody(), as far as I understand from TinyMCE docs, is a function that returns document's body element to be inspected for some features. Problem doesn't occur when I use Safari, nor when I use Firefox with the same site running from localhost.
Original, failing JavaScript-related code looked like this:
<script type="text/javascript" src="http://static.alfa.foo.pl/json2.js"></script>
<script type="text/javascript" src="http://static.alfa.foo.pl/jquery.js"></script>
<script type="text/javascript" src="http://static.alfa.foo.pl/jquery.ui.js"></script>
<script type="text/javascript" src="http://static.alfa.foo.pl/tiny_mce/tiny_mce.js"></script>
<script type="text/javascript">
tinyMCE.init({ mode:"specific_textareas", editor_selector:"mce", theme:"simple", language:"pl" });
</script>
<script type="text/javascript" src="http://static.alfa.foo.pl/jquery.jeditable.js"></script>
<script type="text/javascript" src="http://static.alfa.foo.pl/jquery.tinymce.js"></script>
<script type="text/javascript" charset="utf-8" src="http://static.alfa.foo.pl/foo.js"></script>
<script type="text/javascript">
$(document).ready(function(){
/* jQuery initialization */ });
</script>
I tried changing script loading order, moving tinyMCE.init() call to the <script/> tag containing $(document).ready() call—before, after, and inside this call. No result. When tinyMCE.init() was called from within $(document).ready() handler, the browser did hang on request—looks like it was too late to call the init function.
Then, after googling a bit about using TinyMCE together with jQuery, I changed tinyMCE.init() call to:
tinyMCE.init({ mode:"none", theme:"simple", language:"pl" });
and added following jQuery call to the $(document).ready() handler:
$(".mce").each( function(i) { tinyMCE.execCommand("mceAddControl",true,this.id); });
Still the same error. But, and here's where things start to look like real voodoo, when I added alert(i); before the tinyMCE.execCommand() call, alerts were given, and TinyMCE textareas were initialized correctly. I figured this can be a matter of delay introduced by waiting for user dismissing the alert, so I introduced a second of delay by changing the call, still within the $(document).ready() handler, to following:
setTimeout('$(".mce").each( function(i) { tinyMCE.execCommand("mceAddControl",true,this.id); });',1000);
With the timeout, TinyMCE textareas initialize correctly, but it's duct taping around the real problem. The problem looks like an evident race condition (especially when I consider that on the same browser, but when server is on localhost, problem doesn't occur). But isn't JavaScript execution single-threaded? Could anybody please enlighten me as to what's going on here, where is the actual problem, and what can I do to have it actually fixed?
The browser executes scripts in the order they're loaded, not written. Your immediate scripts -- tinyMCE.init(...) and $(document.ready(...)); -- can execute before the files finish loading.
So, the problem is probably network latency -- especially with 6 separate scripts (each requiring a different HTTP conversation between the browser and server). So, the browser is probably trying to execute tinyMCE.init() before tiny_mce.js has finished being parsed and tinyMCE is fully defined.
If don't have Firebug, get it. ;)
It has a Net tab that will show you how long it's taking all of your scripts to load.
While you may consider the setTimeout to be duct taping, it's actually a decent solution. Only problem I see is that it assumes 1 second will always fix. A fast connection and they could see the pause. A slow connection and it doesn't wait long enough -- you still get the error.
Alternatively, you might be able to use window.onload -- assuming jQuery isn't already using it. (Can anyone else verify?)
window.onload = function () {
tinyMCE.init(...);
$(document).ready(...);
};
Also, was that a direct copy?
<script type="text/javascript">
$(document).ready(function(){
/* jQuery initialization */ }
</script>
It's missing the ) ending ready:
<script type="text/javascript">
$(document).ready(function(){
/* jQuery initialization */ })
</script>
Missing punctuation can cause plenty of damage. The parser is just going to keep reading until it finds it -- messing up anything in between.
Since this is the first page which came in google when I asked myself the same question, this is what i found about this problem.
source
There's a callback function in tinyMCE which is fired when the component is loaded and ready. you can use it like this :
tinyMCE.init({
...
setup : function(ed) {
ed.onInit.add(function(ed) {
console.log('Editor is loaded: ' + ed.id);
});
}
});
If you are using jquery.tinymce.js then you don't need tiny_mce.js because TinyMCE will try to load it with an ajax request. If you are finding that window.tinymce (or simply tinymce) is undefined then this means that the ajax is not yet complete (which might explain why using setTimeout worked for you). This is the typical order of events:
Load jquery.js with a script tag (or google load).
Load TinyMCE's jQuery plugin, jquery.tinymce.js, with a script tag.
Document ready event fires; this is where you call .tinymce(settings) on your textareas. E.g.
$('textarea').tinymce({ script_url: '/tiny_mce/tiny_mce.js' })
Load tiny_mce.js this step is done for you by TinyMCE's jQuery plugin, but it could happen after the document ready event fires.
Sometimes you might really need to access window.tinymce, here's the safest way to do it:
$(document).tinymce({
'script_url': '/tiny_mce/tiny_mce.js'
'setup': function() {
alert(tinymce);
}
});
TinyMCE will go so far as to create a tinymce.Editor object and execute the setup callback. None of the editor's events are triggered and the editor object created for the document is not added to tinymce.editors.
I also found that TinyMCE's ajax call was interfering with my .ajaxStop functions so I also used a setTimeout:
$(document).tinymce({
'script_url': '/tiny_mce/tiny_mce.js'
'setup': function() {
setTimeout(function () {
$(document).ajaxStart(function(e) {/* stuff /});
$(document).ajaxStop(function(e) {/ stuff */});
}, 0);
}
});

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