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Overriding Core Drupal JS Function To Remove Behavior, Should I Edit Property, Or Leave Override Function Empty?

We have a use case where we need to block Drupal's core ajax error handling from alerting users (we're handling the error reporting on our own). Previously another developer had commented out a line in the core ajax.js file, to prevent Drupal from spawning the alert box, but I'd like to handle it without touching core.
From the core, drupal.js:
/**
* Displays a JavaScript error from an Ajax response when appropriate to do so.
*/
Drupal.displayAjaxError = function (message) {
// Skip displaying the message if the user deliberately aborted (for example,
// by reloading the page or navigating to a different page) while the Ajax
// request was still ongoing. See, for example, the discussion at
// http://stackoverflow.com/questions/699941/handle-ajax-error-when-a-user-
// clicks-refresh.
if (!Drupal.beforeUnloadCalled) {
alert(message);
}
};
My current fix, is to override the Drupal.displayAjaxError function and change the Drupal.beforeUnloadCalled property that determines whether or not to alert the error:
var ajax_error_backup = Drupal.displayAjaxError;
Drupal.displayAjaxError = function (message) {
Drupal.beforeUnloadCalled = true;
ajax_error_backup(message);
};
My question, is whether or not this is an appropriate fix? I know that I could also override the function and just leave it empty - costing fewer lines, and not invoking another call to the original function (and saving the object I've created by backing up the original in ajax_error_backup).
Am I adding complexity to keep things tidy, or should I just override with:
Drupal.displayAjaxError = function (message) {
//empty
};
To clarify - the desire is to never have this ajax alert occur, so there's not functional difference between my desire to keep things neat/tidy, and just overriding the function with a blank one - there isn't a case where want this alert to succeed.
Thanks in advance for helping this old dog think through something with fresh eyes.

In this case, there isn't one option that seems to be clearly better than the other. It should be handled on a case by case basis, and in this case, either of the methods really is adequate.
I personally opted for using the slightly more expensive method of overriding the function and calling it back, because I felt that it might be somewhat more future-proof:
var ajax_error_backup = Drupal.displayAjaxError;
Drupal.displayAjaxError = function (message) {
Drupal.beforeUnloadCalled = true;
ajax_error_backup(message);
};
If Drupal were to extend the function on their end in the future, there might be another condition that we wouldn't want to override.
Overriding with the empty function would be the cheapest, but would also potentially be a bit heavy handed.
It seems that either approach is valid, and is probably best handled case-by-case.

How to re-evaluate a script that doesn't expose any global in a declarative-style component

I have been writing a reusable script, let's call it a plugin although it's not jQuery, that can be initialised in a declarative way from the HTML. I have extremely simplified it to explain my question so let's say that if a user inserts a tag like:
<span data-color="green"></span>
the script will fire because the attribute data-color is found, changing the color accordingly.
This approach proved very handy because it avoids anyone using the plugin having to initialise it imperatively in their own scripts with something like:
var elem = document.getElementsByTagName('span')[0];
myPlugin.init(elem);
Moreover by going the declarative way I could get away without defining any global (in this case myPlugin), which seemed to be a nice side effect.
I simplified this situation in an example fiddle here, and as you can see a user can avoid writing any js, leaving the configuration to the HTML.
Current situation
The plugin is wrapped in a closure like so:
;(function(){
var changeColor = {
init : function(elem){
var bg = elem.getAttribute('data-color');
elem.style.background = bg;
}
};
// the plugin itslef looks for appropriate HTML elements
var elem = document.querySelectorAll('[data-color]')[0];
// it inits itself as soon as it is evaluated at page load
changeColor.init(elem);
})();
The page loads and the span gets the correct colour, so everything is fine.
The problem
What has come up lately, though, is the need to let the user re-evaluate/re-init the plugin when he needs to.
Let's say that in the first example the HTML is changed dynamically after the page is loaded, becoming:
<span data-color="purple"></span>
With the first fiddle there's no way to re-init the plugin, so I am now testing some solutions.
Possible solutions
Exposing a global
The most obvious is exposing a global. If we go this route the fiddle becomes
http://jsfiddle.net/gleezer/089om9z5/4/
where the only real difference is removing the selection of the element, leaving it to the user:
// we remove this line
// var elem = document.querySelectorAll('[data-color]')[0];
and adding something like (again, i am simplifying for the sake of the question):
window.changeColor = changeColor;
to the above code in order to expose the init method to be called from anywhere.
Although this works I am not satisfied with it. I am really looking for an alternative solution, as I don't want to lose the ease of use of the original approach and I don't want to force anyone using the script adding a new global to their projects.
Events
One solution I have found is leveraging events. By putting something like this in the plugin body:
elem.addEventListener('init', function() {
changeColor.init(elem);
}, false);
anybody will be able to just create an event an fire it accordingly. An example in this case:
var event = new CustomEvent('init', {});
span.dispatchEvent(event);
This would re-init the plugin whenever needed. A working fiddle is to be found here:
http://jsfiddle.net/gleezer/tgztjdzL/1/
The question (finally)
My question is: is there a cleaner/better way of handling this?
How can i let people using this plugin without the need of a global or having to initialise the script themselves the first time? Is event the best way or am I missing some more obvious/better solutions?

You can override Element.setAttribute to trigger your plugin:
var oldSetAttribute = Element.prototype.setAttribute;
Element.prototype.setAttribute = function(name, value) {
oldSetAttribute.call(this, name, value);
if (name === 'data-color') {
changeColor.init(this);
}
}
Pros:
User does not have to explicitly re-initialize the plugin. It will happen automatically when required.
Cons:
This will, of course, only work if the user changes data-color attributes using setAttribute, and not if they create new DOM elements using innerHTML or via some other approach.
Modifying host object prototypes is considered bad practice by many, and for good reasons. Use at your own risk.

Dynamically Included Javascript and Dependencies

So, as a sort of exercise for myself, I'm writing a little async script loader utility (think require.js, head.js, yepnope.js), and have run across a little bit of a conundrum. First, the basic syntax is like this:
using("Models/SomeModel", function() {
//callback when all dependencies loaded
});
Now, I want to know, when this call is made, what file I'm in. I could do it with an ajax call, so that I can mark a flag after the content loads, but before I eval it to mark that all using calls are going to be for a specific file, then unset the flag immediately after the eval (I know eval is evil, but in this case it's javascript in the first place, not json, so it's not AS evil). I'm pretty sure this would get what I need, however I would prefer to do this with a script tag for a few reasons:
It's semantically more correct
Easier to find scripts for debugging (unique file names are much easier to look through than anonymous script blocks and debugger statements)
Cross-domain requests. I know I could try to use XDomainRequest, but most servers aren't going to be set up for that, and I want the ability to reference external scripts on CDN's.
I tried something that almost got me what I needed. I keep a list of every time using is called. When one of the scripts loads, I take any of those using references and incorporate them into the correct object for the file that just loaded, and clear the global list. This actually seems to work alright in Firefox and Chrome, but fails in IE because the load events seem to go off at weird times (a jQuery reference swallowed a reference to another type and ended up showing it as a dependency). I thought I could latch on to the "interactive" readystate, but it doesn't appear to ever happen.
So now I come asking if anybody here has any thoughts on this. If y'all want, I can post the code, but it's still very messy and probably hard to read.
Edit: Additional usages
//aliasing and multiple dependencies
using.alias("ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js", "jQuery");
using(["jQuery", "Models/SomeModel"], function() {
//should run after both jQuery and SomeModel have been loaded and run
});
//css and conditionals (using some non-existant variables here)
using.css({ src: "IEFix", conditionally: browser === "MSIE" && version < 9 });
//should include the IEFix.css file if the browser is IE8 or below
and to expound more on my response below, consider this to be file A (and consider the jquery alias from before to be there still):
using(["jQuery", "B"], function() {
console.log("This should be last (after both jQuery and B have loaded)");
console.log(typeof($));
});
Then this would be B:
using("C", function() {
console.log("This should be second");
});
And finally, C:
console.log("This should be first");
The output should be:
This should be first
This should be second
This should be last (after both jQuery and B have loaded)
[Object Object]

Commendable that you are taking on such an educational project.
However, you won't be able to pull it off quite the way you want to do it.
The good news is:
No need to know what file you are in
No need to mess with eval.
You actually have everything you need right there: A function reference. A callback, if you will.
A rough P-code for your using function would be:
function using(modules, callback) {
var loadedModules = []
// This will be an ajax call to load things, several different ways to do it..
loadedModules[0] = loadModule(modules[0]);
loadedModules[1] = loadModule(modules[1]);
// Great, now we have all the modules
// null = value for `this`
callback.apply(null, loadedModules);
}

#Font-face and wrong value of the offsetWidth attribute

I encounter this problem in the latest version of Chromium. After the creation of the first element using a font-family embedded via #font-face I am being handed wrong offsetXyz values. By the time the script is executed, the window.onload hook will already have fired and the font will thus have already been loaded.
This is what the script looks like (schematically):
var e = document.createElement("span");
e["innerText" in e?"innerText":"textContent"] = "fooBar";
e.style.fontFamily = "fontFaceEmbeddedFontFamily";
document.body.appendChild(e);
alert(e.offsetWidth); // Returns two different values
setTimeout(function() {
alert(e.offsetWidth); // The latter being correct
}, 1000);
The value is updated "silently". There appears to be no way of waiting for it to correct the values but simply setInterval-check the value and then render the solution. I don't fancy doing dirty stuff like that.
Anyone has any suggestions how to proceed? Happens only when the src: local(" ... ") isn't specified, the issue is hence downloaded-font specific.

You have already given the answer yourself. Set src: local() and it will not happen - in general when you use #font-face, stick to the bulletproof syntax, since it was made to overcome browser issues like the one you are butting heads with here.

I know is almost a year, but I got this problem too and took me half a day to discover the cause. You can just wait for the entire page to load, instead of using a timeout. The src: local() didn't make any difference for me. So you can use:
<body onload="finished()">
or in jQuery:
$(window).load(
function() {
// this only will execute when the entire page is loaded.
}
);

Watch for a property creation event?

I need to be able to determine when an object is created (not a DOM element -- a JavaScript object).
An answer to this question has some very useful looking code for creating observable properties, so you can have a function fire when a property changes.
In my situation I need to do something when the object/property is created, not an existing property changed, and my limited understanding of such matters did not help me figure out if or how I could use that code to do this after much squinting.
The situation is: page loads a bunch of scripts. Some of the scripts create things that are needed by other scripts, e.g:
ThisStuff = (function () {
// blah blah
return self;
} ());
Some other code needs to initialize this ThisStuff, whenever it's available, which may be after the DOM is done loading. The user doesn't actually need ThisStuff right away, so it's fine for it to happen whenever the script is done loading. So I would like to do something along lines of:
$(document).ready(function() {
wheneverIsAvailable(window,'ThisStuff', function(object) {
object.init(args);
})
});
I realize there are other solutions to this problem (changing script order, or loading scripts on demand) but those are difficult because of the architecture. So I'm only interested in a way to do this versus other solutions. If jQuery offers some such functionality, that's fine also as I'm using it.

You could have a setInterval checking a number of times a second to watch the specific variable. You can check whether it is created using obj.hasOwnProperty(prop). When it is created, you invoke the function, and clear the interval.
It might be dirty but it might also just work fine for you.
Edit: I coded this for you: http://jsfiddle.net/jhXJ2/2/. It also supports passing additional arguments to the function.
window.__intervals = [];
function wheneverIsAvailable(obj, prop, func) {
var id = (Math.random()+"").substring(2);
var args = arguments;
window.__intervals[id] = window.setInterval(function() {
if(obj.hasOwnProperty(prop)) {
window.clearInterval(window.__intervals[id]);
func(Array.prototype.slice.call(args, 3));
// Call function with additional parameters passed
// after func (from index 3 and on)
}
}, 1000/ 50);
}
wheneverIsAvailable(window, 'test', function() {
alert(arguments[0]);
}, 'Woot!');
window.setTimeout('window.test = 123', 1000);

This is a bit far-fetched but it might work.
You would need to use knockoutjs, a javascript library. It's awesome but is built for a slightly different purpose.
Anyways it has a dependentObservable thing which allows to fire up an event whenever a certain value changes. Now I know you want on creation but you can check whether your variable holds any value (other than what you provided initially), if yes then consider it initialize.
Let me know if you think this sounds feasible.