Develop Reference

How can I execute a JavaScript function on the first page load?

I am wondering if there is a way to execute a JavaScript function once only on the first ever page load and then not execute on any subsequent reloads.
Is there a way I can go about doing this?

The code below will execute once the onload event fires. The statement checks if the onetime function has NOT been executed before by making use of a flag (hasCodeRunBefore), which is then stored in localStorage.
window.onload = function () {
if (localStorage.getItem("hasCodeRunBefore") === null) {
/** Your code here. **/
localStorage.setItem("hasCodeRunBefore", true);
}
}
Note: If the user clears their browsers' localStorage by any means, then the function will run again because the flag (hasCodeRunBefore) will have been removed.
Good news...
Using localStorage can be tedious because of operators and long winded function names. I created a basic module to simplify this, so the above code would be replaced with:
window.onload = function () {
if (!ls.exists('has_code_run_before')) {
/** Your code here... **/
ls.set.single('has_code_run_before', true);
/** or... you can use a callback. **/
ls.set.single('has_code_run_before', true, function () {
/** Your code here... **/
});
}
};
Update #1
Per #PatrickRoberts comment, you can use the in operator to see if a variable key exists in localStorage, so
if (localStorage.getItem('hasCodeRunBefore') === null)
becomes
if (!('hasCodeRunBefore' in localStorage))
and is less verbose and a lot cleaner.
Secondly, you can set values as you would an object (localStorage.hasCodeRunBefore = true) though it will be stored as a string, not as boolean (or whatever data type your value is).

function toBeExecutedOnFirstLoad(){
// ...
}
if(localStorage.getItem('first') === null){
toBeExecutedOnFirstLoad();
localStorage.setItem('first','nope!');
}

All JavaScript must execute every time a page loads. If the script is on the page, it will execute.
The logic that is executed within the JavaScript included on the page may execute in a different manner depending on the page state, input provided, and any other signals it receives, be it from the server or the client.
If you're using a server side language, you might choose to render a script conditionally, such as the first time a user logs in.
If you need to include the javascript irrespective of context, then you need to listen to other signals.
The simple modern solution is to make use of localStorage. localStorage can be used to store custom string values on custom key values for any given domain.
The code to make use of this would look like:
if (localStorage['...my key here...'] === '...my expected value here...') {
// The page has been visited before
} else {
// The page has not been visited before
// OR
// The user or script has cleared the localStorage value
}
localStorage['...my key here...'] = '...my expected value here...';
That's all well and good if you just need things to work on the client alone. Sometimes you might need the server to know whether or not the page has been visited before.
The (less)simple solution is to use document.cookie:
if (/(?:^|;\s*)...my key here...=...my expected value here...(?:;|$)/.test(document.cookie)) {
// the page has been visited before
} else {
// The page has not been visited before
// OR
// The user or script has cleared the cookie
}
document.cookie = '...my key here...=...my expected value here...';
If you need to defer the execution until the page has finished loading, then simply include the script in an onload callback, either by assigning the event to the window:
window.onload = function () {
// do stuff when the page has loaded
//this will override any other scripts that may have been assigned to .onload
};
or by binding the event handler to the window:
window.addEventListener('load', function () {
// do stuff when the page has loaded
}, false);

It depends on what first page load means to you. It's subjective.
If you want the function to fire once the DOM has been parsed, but only the HTML and no other external resources, bind it to the DOMContentLoaded event.
document.addEventListener('DOMContentLoaded', fn);
Otherwise, if you want to wait for external resources to be loaded and then fire the event, you should bind it to the window object's load event like so:
window.addEventListener('load', fn);
Here are some links from the Mozilla Developer Network that explain the what I just said in more detail:
https://developer.mozilla.org/en-US/docs/Web/Events/load
https://developer.mozilla.org/en-US/docs/Web/Events/DOMContentLoaded
Good luck!

I was facing something similar, the difference in my case was, I wanted to run a code whenever a new instance was being created I needed a certain code to execute, and then later for the rest of the reloads that code should not execute.
For that similar to localStorage solutions above use session storage instead:
fun_RunOnlyOnFirstPageLoad(){}
if(!$window.sessionStorage.getItem(hasRunBefore)){
fun_RunOnlyOnFirstPageLoad();
$window.sessionStorage.setItem(hasRunBefore, true);
}
using the window.sessionStorage instead stores the value only for that session.
this way once the tab is closed (session is over, that value is wiped out) and on every new instantiation, the code is executed.

Ajax .load() won't work when triggered initially

So I have a simple tab system which I handle with the .load function to load the desired content. The problem is that the page itself which contains this tab system is a ajax loaded content. And for some reason the initial call of the tab function to display the initial tab content won't work. But after manually choosing a tab, the load function loads the content properly.
her some code to look at:
The tab handler:
function loadTab(tab) {
$(".tab_a:eq("+otab+")").removeClass("tab_slc");
$('#tab_content').hide();
$('#tab_content').load("include/tab_downloadVersions.html .tab:eq("+tab+")");
$(".tab_a:eq("+tab+")").addClass("tab_slc");
$('#tab_content').fadeIn(function() {});
otab = tab;
}
at the end I call loadTab(tab); and the thing should be initialized. but for some reason the content remains empty. As soon as you manually click on a tab (I have an on click function which calls loadTab(tab) everything starts working)
Because the code by itself works, I think the problem is caused by the other script which handles the page itself. It is also a .load function which loads the page, which loads this tab system.
So do multiple .loads don't like each other? and if so, what can I change?
Thanks in advance ;)
EDIT: I could't post the entire code for some reason, but if you go here you can see the site in action with all the scripts:
n.ethz.ch/student/lukal/paint.net
The tab system is on the download page.
EDIT:-----------------------------------------------------------------------------------------------------------------------------
Big Update
So this is still the same issue but with a slight twist: I did what was recommended in the comments and put my secondary .load() call inside the success call of the first one.
$("#content").load("pages/contact #contentInside", function() {
$("#OtherContent").load("include/info #OtherContentInside");
});
So this works.
But now I had the great idea to make a giant load function. It is a slightly better function than just the plain load, cause it does some fading and stuff. But now I have the same problem, but even more complicated. I created the load function as a "plugin" so the function itself is in a different script file and therefore I can't access the inside of the success function. I solved this problem with a return $.ajax(); and a .done() call. The problem here is that there is some rare case where it just skips the secondary load function. So I am searching for a guaranteed way of controlling the order of the .load calls. Any idea?
The mock-up website is up to date with the new scripts if you wish to take a look. And people were complaining about potential virus spread from my link. For some reason I can't post long code snippets so the site is the best source I got to show everything. If you know a more trustworthy way to share my code please let me know.

We cannot see the rest of your code to tell where the initial call is being invoked from. A set up like the following should work:
$(function() {
var tab = 0;
loadTab( tab );
});
function loadTab(tab) {
//WHAT IS otab???
$(".tab_a:eq("+otab+")").removeClass("tab_slc"); //<<<==== otab
$('#tab_content').hide();
$('#tab_content').load("include/tab_downloadVersions.html .tab:eq("+tab+")");
$(".tab_a:eq("+tab+")").addClass("tab_slc");
$('#tab_content').fadeIn(function() {});
otab = tab;
}
Update
The reason it does not work initial is because otab is not defined the first time the function is called. You have initialized otab at the end of the function but you are using it at the beginning of the function.
UPDATE 2
I have had a chance to look at your code and I just found out what the issues are:
You do not have DOM ready
You are not calling the function on page load.
The following version of your code should work -- try not to use global variable as you're doing with otab. Since you're loading this script at the end of the page (an you are using event delegation) you may get away with DOM ready. Adding .trigger('click') or click() as indicated below should resolve the issue.
//Tab-loader
//Haeri Studios
var tab = 0;
var otab = tab;
var counter = 0;
//click detect
$(document).on('click', '.tab_a', function() {
tab = counter == 0 ? tab : ($(this).attr('id'));
loadTab(tab);
counter++;
return false;
})
.trigger('click'); //<<<<<===== This will call the function when the page loads
//Tab setup
function loadTab(tab) {
//Content Setup
$(".tab_a:eq("+otab+")").removeClass("tab_slc");
$('#tab_content').hide();
$('#tab_content').load("include/tab_downloadVersions.html .tab:eq("+tab+")");
$(".tab_a:eq("+tab+")").addClass("tab_slc");
$('#tab_content').fadeIn(function() {});
otab = tab;
}
//Initialize << WHAT ARE YOUR INTENTIONS HERE .. DO YOU REALLY NEED THIS PIECE?
$.ajax({success: function() {
loadTab(tab);
}});

A partial answer to this problem was to call the loadTab function inside the success call of the page load function, like charlietfl pointed out. But the problem is that there is no need to call the tabloader every time a new page gets called. So I would rather not have a rare call in every page setup function.

I am a bit disappointed by the system on stackoverflow. It seems like if you have not a high reputation level, no one gives a "S" about your questions. Well but at least some input was give, for which I am very thankful.
So by digging deeper into google I found out that the callback can be manually placed in the function where ever you like.
so if we have a function:
foo(lol, function() {
//This after
});
this does stuff after foo() is done. But what if we have another function inside foo() which we also need to wait for:
function foo(lol) {
bar(troll, function() {
//This first
});
}
The bar function is not relevant to the success call of foo. This causes the unpredictable outcome of calls.
The trick is to control when the success function of foo gets called.
If we add a parameter(callback) inside foo and call this "parameter" (callback();) inside the success call of bar, we can make sure the order is guaranteed.
And that's it:
function foo(lol, callback) {
bar(troll, function() {
//This first
callback(); //<-This callback placement defines when it should be triggered
});
}
foo(lol, function() {
//This after
});
We get:
//this first
//this after

jQuery recursion

I have a problem with my code, some code does not work when I call recursive call of same function inside it. It has to be something with myGalleria = Galleria.get(0);, but I have no idea how to make it all work.
Document Ready (just to show when I call function for the first time, everything works fine for first time)
$(document).ready(function(){
$.getJSON('getImages.php', {
cat: "123"
}, function(imgData){
createGallery(imgData);
});
});
Now function itself, note that when I click on .galleria-menuButtons span that calls same function nothing is working, well galleria itself is creating, but nothing else.
function createGallery(imgData){
$("#gallery").galleria({
image_margin: 30,
clicknext: true,
transition: "fade",
dataSource: imgData
});
myGalleria = Galleria.get(0); // I don't think this works after recursive call
// Adding menu and menu buttons
myGalleria.addElement("menu").appendChild("container", "menu");
myGalleria.addElement("menuButtons").appendChild("menu", "menuButtons");
$.ajax({
url: "menuButtons.php",
success: function(data){
myGalleria.$("menuButtons").html(data);
}
});
// Menu button click events
$('.galleria-menuButtons span').live('click', function(){
alert(this.id);
// Getting jSon data
$.getJSON('getImages.php', {
cat: this.id
}, function(imgData) {
alert(imgData);
createGallery(imgData); // <- Recursive call
});
});
}
I have similar function on window.resize and it also does not work after recursive call.
$(window).resize(function(){
$(".galleria-container").css("width", $(window).width());
$(".galleria-container").css("height", $(window).height());
galleriaRescale = Galleria.get(0);
galleriaRescale.rescale(); // <- this is not working either
//sizeBG();
});

FYI - this isn't actually recursion in the traditional sense because you're calling createGallery from a click handler which launches a JSON request which then calls createGallery when that succeeds, both of which will occur after the previous call to createGallery finishes.
But you do have surviving function closures which could be confusing things or causing problems. One guess is that you may want to make sure that things you expect to be local variables (like myGalleria have a var in front of them so they really are local variables and not variables that might be scoped to a higher level and be influenced by a previous incarnation of this call or be influencing an earlier call that hasn't yet completed.
var myGalleria = Galleria.get(0);
Then, assuming imgData is some sort of data structure like an array or object, you have to make sure that there's either only one global version of that data structure that never changes or that each call of createGallery has the appropriate separate copy of that data structure. If it's getting changed along the way, then subsequent calls to createGallery may not be getting the data they want. If it's a read-only data structure (you don't change it), then you're probably OK on that one.
OK, let's talk through the pseudo code for what this does.
On page ready, you get some JSON image data.
When that succeeds, you call createGallery with that image data.
The createGallery call does some sort of operation in the DOM (perhaps an animation)
It then calls: myGalleria = Galleria.get(0); Because there is no var in front of myGalleria, this is a global variable declaration (bad news for recursion and closures)
You then use the myGalleria data structure to make some changes to the DOM (adding menus and menu items).
You then add a .live click handler on a pretty generic set of CSS classes (it's possible you have added this click handler more than once here).
You then fetch some JSON image data again.
When that image data is fetched, you start the whole process over again by called createGallery.
Summary
The two potential problems I see are that myGalleria is not a local variable and probably should be and you may be adding duplicate click handlers.
If neither of these fully solve the issue, then we probably need more information about what Galleria.get(0) is doing.
FYI, the resize clickHandler looks like it may have the same issue with not using var to make your variable declaration a local variable.
Round 2
OK, here are some more observations.
When you add the menu and menu buttons with this block of code, you aren't providing any unique identifiers to either the addElement or appendChild functions (you're providing "menu" and "menuButtons" to both). As such, I don't know how you can uniquely hook up to them in the subsequent click event. As far as your code looks, all the menu items look identical and none have unique state. I don't know the Galleria code, but I assume somebody has to make unique identifiers for these new items so that you can uniquely identify them in your subsequent click handler.
// Adding menu and menu buttons
myGalleria.addElement("menu").appendChild("container", "menu");
myGalleria.addElement("menuButtons").appendChild("menu", "menuButtons");
When you set up a click handler to presumably handle the clicks for just these menu items, you are using the exact same CSS selector every time so there's no way that this click handler is going to be uniquely assigned to just the newly create menu items (which is what I assume you want). I don't know the Galleria code, but I assume that you should create some sort of unique ID that you pass into addElement and appendChild for the newly created menu items and then reference that unique identifier when you install the click handler. Likewise, this function needs to uniquely target just the menu buttons you created by using unique identifiers myGalleria.$("menuButtons").html(data);
Lastly, I'd suggest you change the name of one of your variables just to avoid confusion. In your click handler, change the three occurrences of imgData to just data so there can be no confusion about closures and the value of imgData.
Round 3
Ultimately one of the fixes was this (embedded in the comments):
I think it might work if you just only install the .live click handler once outside the createGallery function rather than call it each time. Since it's .live it will automatically work for all future buttons you create so you should only call it once. I'd suggest putting it in the $(document).ready function block.

Having a callback when a function is called without touching the actual function (jquery)?

I'm developing a small plugin that changes the favicons if there are unread messages in mailbox in Roundcubemail. However, the API sucks, and the event listupdate is fired only when the whole page is loaded, even if it is meant to fire when the list is updated.
However, I've managed to find out, that every time the list is updated, certain functions are called, such as set_unread_count. It gets the unread-count easily, so it would be great to somehow "append" stuff to this function. I just think based on hours of searching that there is no solution for this. Can I add a callback to be called when the set_unread_count is called? Can I somehow append stuff to that function? Any other ideas?

Create a little hook.
var _old_set_unread_count = set_unread_count;
set_unread_count = function() {
// do whatever you want here
// access arguments[x] to get arguments.
_old_set_unread_count.apply(this, arguments);
};
Demo: http://www.jsfiddle.net/4yUqL/69/

Create new window using jquery

I'm working on a little project in JavaScript/jQuery.
In order to display results from a calculation done in javascript, I'd like to open a new window with some predefined content and modify this content in order to display the results: Im using code like this:
var resultwindow = window.open('result.html')
var doc = $('body', resultwindow.document);
doc.append("<p>Result</p>")
This is not working since the result document is not yet loaded when I append the content, so it is overwritten with the contents of 'result.html'.
I also tried
$(resultwindow.document).ready(function() {
// ... Fill result document here
})
and
$(resultwindow.document).load(function() {
// ... Fill result document here
})
but ready() works only on the current document (it is called immediately, if the current document is already loaded), and load doesn't get called at all.
Perhaps someone can point me to the right direction. Thanks in advance!
EDIT:
I finally solved this by creating the new document "by hand" in Javascript like:
w = window.open('','newwinow','width=800,height=600,menubar=1,status=0,scrollbars=1,resizable=1);
d = w.document.open("text/html","replace");
d.writeln('<html><head>' +
'<link rel="stylesheet" type="text/css" href="style.cs"/></head>' +
+'<body></body></html>');
// use d to manipulate DOM of new document and display results
If I were to do the same thing today (two years of experience later), I'd use some Javascript template library like Handlebars to maintain a template and compile it to javscript.

Your load call doesn't work because you're attempting to handle the load of the document, and chances are document does not even exist at this point. Which means you are passing null into jQuery, and it gracefully ignores you. Handle the load event of the raw window reference instead, and then you should be good to go...
var win = window.open("result.html");
$(win).load(function() {
$("body").append("<p>Result</p>");
});

The problem you have is that load() doesn't do what you think it does.
Instead, use bind("load", function() { /* Your function here */ }); then everything should work.
Correction:
load() is actually a dual-use function -- if it's called with a function as its first parameter, then it binds it to the load event of the object (or objects) in question, otherwise it loads the returned data (if any) into the elements in question. See Josh's answer for the real reason why it's not working.

Send the data to result.html in the querystring and then have the result.html display the data from there. If you want to be less obvious about it going through you could hash the data in the querystring and have the result page dehash it.