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Attaching an Event to an element and dispatching it correctly

I need to attach an Event called render to a panel element, that does nothing but being dispatched to warn all the listeners whenever panel is rendering.
Following the The old-fashioned way section of this link, I came up with this code:
/**
* **Static** Re-draw the layer panel to represent the current state of the layers.
* #param {Element} panel The DOM Element into which the layer tree will be rendered
*/
static renderPanel(panel) {
// Create the event.
var render_event = document.createEvent('Event');
// Define that the event name is 'render'.
render_event.initEvent('render', true, true);
// Listen for the event.
panel.addEventListener('render', function (e) {
// e.target matches panel
}, false);
panel.dispatchEvent(render_event);
This seems to have worked but as this is my first time doing this, I am not quite sure how to check the correctness of this method.
Looking inside the console I can see my panel element dispatching the render Event, but I'd like to ask if there's something I am missing or to be worried about before moving on.
To debug the result, I tried add an event listener to the document element like document.addEventListener("render",console.log("ciao")), which in turn printed ciao once in the console, but only just once.
I thought I would be able to see as many "ciao" in the console as the times the render Event was triggered, but this does not seem the case.

If you're trying to check everytime your event is fired, the second argument of addEventListener (taking into account what you're willing to achieve) should be a function callback using an event object as argument, like this for example:
document.addEventListener("render", function(e) { console.log("ciao"); });
In your example you're executing console.log("ciao"), not passing a function reference (anonymous or not), this is why it executes only one time: when the page loads/evaluates your script.

mdn guide on creating and dispatching custom events (same as your link)
The old fashioned method seems to still be working fine when I tried it, I saw the document event listener console log each time I triggered the event.
The updated way is:
panel.dispatchEvent(new CustomEvent('render'));
let div = document.querySelector('div');
div.addEventListener('old-event', () => {console.log('Old-fashinoed event caught')});
div.addEventListener('new-event', () => {console.log('New-fashioned event caught')});
let oldEvent = document.createEvent('Event');
oldEvent.initEvent('old-event', true, true);
let newEvent = new CustomEvent('new-event');
setInterval(() => {
div.dispatchEvent(oldEvent);
div.dispatchEvent(newEvent);
}, 1000);
<div>I emit an old-fashioned and a new-fashioned event every 1 second</div>

How to resolve StaleElementReference in Mocha.js + Selenium + wd.js

I'm writing automation tests for a website using Mocha + SeleniumServer + wd.js + chai-as-promised.
The website uses JavaScript for the front-end which seems to refresh the elements on the page when certain action is performed. i.e. Upon selecting an element in a grid, the "next" button is enabled to allow user to move on to the next page. It seems that this changes the reference to the button element resulting in the StaleElementReference error.
describe('1st step', function () {
it('should select an element is grid', function () {
return browser
.waitForElementByCss('#grid', wd.asserters.isDisplayed, 20000)
.elementByCss('#grid .elementToBeSelected')
.click()
.sleep(1000)
.hasElementByCss('#grid elementToBeSelected.active')
.should.eventually.be.true;
});
it('should proceed next step', function () {
return browser
.waitForElementByCss('.btnGrid .btn.nextBtn:not(.disabled)', wd.asserters.isDisplayed, 20000)
.elementByCss('.btnGrid .btn.nextBtn:not(.disabled)')
.click()//Error thrown here
.sleep(2000)
.url()
.should.eventually.become('http://www.somewebsite.com/nextpage');
});
});
With my limited experience with JavaScript, I have tried all that i could think off, but to no avail. So is there anyway I can avoid this StaleElementReference error? Also, the error is only sometimes thrown during execution.

You might want to read some more on the Stale Element Reference exception. From what you are describing, it sounds like you get a reference to an element, do something on the page which then changes/removes the referenced element. When you do something with the variable reference you get this error. The solution really depends on the code you are using to do your tests and your framework for accessing elements. In general, you need to be aware of when you perform an action that changes the page and refetch the element before you access it. You could always refetch an element before you access it, you could refetch all elements that are affected by a page change, and so on...
You code probably looks something like this
WebElement e = driver.findElement(...); // get the element
// do something that changes the page which, in turn, changes e above
e.click(); // throws the StaleElementReference exception
What you probably want is something more like one of these...
Don't fetch the element until you need it
// do something that changes the page which, in turn, changes e above
WebElement e = driver.findElement(...); // get the element
e.click(); // throws the StaleElementReference exception
...or fetch it again right before you need it...
WebElement e = driver.findElement(...); // get the element
// do something that changes the page which, in turn, changes e above
e = driver.findElement(...); // get the element
e.click(); // throws the StaleElementReference exception
I would prefer the first fix... just fetch what you need when you need it. That should be the most efficient way to solve this problem. The second fix might have performance issues because you might be refetching a bunch of elements over and over and either never using them or refetching them 10 times only to reference the element once at the end.

Automation script is not working?

This is the first time I get my hands on with automation instruments in xcode The script works well for all button taps but the one making server connection. I don't know the reason
Here is the script I tried so far
var target = UIATarget.localTarget();
target.pushTimeout(4);
target.popTimeout();
var window=target.frontMostApp().mainWindow()
var appScroll=window.scrollViews()[0];
appScroll.logElementTree();
UIATarget.localTarget().delay(2);
appScroll.buttons()[1].tap();
The above script works up to showing the UIActivityIndicator instead of moving to next controller after success
I know There must be a very simple point I am missing. So help me out

UIAutomation attempts to make things "easy" for the developer, but in doing so it can make things very confusing. It sounds like you're getting a reference to window, waiting for a button to appear, then executing .tap() on that button.
I see that you've already considered messing with target.pushTimeout(), which is related to your issue. The timeout system lets you do something that would be impossible in any sane system: get a reference to an element before it exists. I suspect that behind-the-scenes, UIAutomation repeatedly attempts to get the reference you want -- as long as the timeout will allow.
So, in the example you've posted, it's possible for this "feature" to actually hurt you.
var window=target.frontMostApp().mainWindow()
var appScroll=window.scrollViews()[0];
UIATarget.localTarget().delay(2);
appScroll.buttons()[1].tap();
What if the view changes during the 2-second delay? Your reference to target.frontMostApp().mainWindow.scrollViews()[0] may be invalid, or it may not point to the object you think you're pointing at.
We got around this in our Illuminator framework by forgetting about the timeout system altogether, and just manually re-evaluating a given reference until it actually returns something. We called it waitForChildExistence, but the functionality is basically as follows:
var myTimeout = 3; // how long we want to wait
// this function selects an element
// relative to a parent element (target) that we will pass in
var selectorFn = function (myTarget) {
var ret = myTarget.frontMostApp().mainWindow.scrollViews()[0];
// assert that ret exists, is visible, etc
return ret;
}
// re-evaluate our selector until we get something
var element = null;
var later = get_current_time() + myTimeout;
while (element === null && get_current_time() < later) {
try {
element = selectorFn(target);
} catch (e) {
// must not have worked
}
}
// check whether element is still null
// do something with element
For cases where there is a temporary progress dialog, this code will simply wait for it to disappear before successfully returning the element you want.

Call Silverlight method from Javascript when it's ready

I have a page that loads another window on button click. The loaded page has silverlight control on it, so it takes some time to load and get prepared before it can receive javascript calls.
What I need to do is to call a particular method of silverlight object right after the silverlight plugin gets loaded and is ready to interact with me.
Now, if the pop-up page was already opened then the code would be like that:
var slWin = window.open('PopupPage.html', 'WindowName');
var elem = slWin.document.getElementById('slControl');
elem.Content.SlObject.MethodA();
This works when the window is already opened because the control is already loaded and ready. I need to modify this code to handle the situation when the elem need some time to be prepared.
I tried to use jQuery's ready and load methods to add handlers to corresponding events, but with no particular lack. Here's the full snippet:
var slWin = window.open('', 'WindowName');
var elem = slWin.document.getElementById('slControl');
if (elem == null) {
slWin.location.href = 'PopupPage.aspx';
// this branch doesn't work
$(slWin).load(function () {
elem = slWin.document.getElementById('slControl');
elem.Content.SlObject.MethodA();
});
}
else {
// this branch works fine
elem.Content.SlObject.MethodA();
}
How do I solve this issue? I don't mind jQuery solutions.

This error is happening because the Silverlight object is not fully loaded when you are trying to access it.
Try to use the "onload" event of the silverlight object to dectect when it's ready to use. Here you have a link to the MSDN documentation:
http://msdn.microsoft.com/en-us/library/cc838107(v=vs.95).aspx
Hope it helps. :)

Tracking Clicks; Performance Implications to Searching the DOM

I have a Javascript plugin that searches the DOM for any elements starting with the class name "tracking" and adds a click event listener (or another type of listener, if specified) to that element. The idea is that every time that event occurs on that element, that it runs a Javascript function that sends data to our traffic servers. Here's what the code looks like:
// Once the page is completed loaded
window.mmload(function() {
// Get the container object
obj = document.getElementById(name);
if ( obj.length < 0 )
throw ("The Id passed into the tracker does not exist ("+name+")");
// Find all the elements belonging to the tracking class
var trackingClass = new RegExp( /tracking\[[a-zA-Z0-9\.\-_]+\]/g );
var myElements = getElementsByRegex( trackingClass, obj );
//For each of those elements...
for( var i in myElements ) {
var elm = myElements[i];
var method = elm.className.match( /tracking\[[a-zA-Z0-9\.\-_]+\]/ )[0].split('[')[1].replace(']','').split('.')[2];
method = typeof( method ) == 'undefined' ? 'click' : method;
// Add a click event listener
myElements[i].addEventListener( method, function(e){
// Get the element, the link (if any), and the args of the event
var link = elm.getAttribute('href') == null ? "" : elm.getAttribute('href');
var args = elm.className.match( /tracking\[[a-zA-Z0-9\.\-_]+\]/ )[0].split('[')[1].replace(']','').split('.');
// If a link existed, pause it, for now
if ( link != '' )
e.preventDefault();
// Track the event
eventTracker( args[0], args[1], ( method == 'click' ? 'redirect' : 'default' ), link );
return false;
}, true);
}
});
Right now I've got this chuck of code running once the window has completely loaded (window.mmload() is a function I made for appending window.onload events). However, there maybe times when I need to run this function again because I added new elements to the DOM via Javascript with this class name and I want to track them too.
My initial solution was to run this function using setInterval to check the DOM every few milliseconds or second or whatever makes the most sense. However, I was worried if I took this approach that it might slow down the website, especially since this is running on a mobile website for smartphones. I'm not sure what kind of a performance hit I might take if I'm searching to DOM every so often.
The other approach I had in mind was to simply call the function after adding traceable elements to the DOM. This is probably the most efficient way of handling it. However, the people that I'm working with, granted very smart individuals, are Web Designers who don't often think about nor understand very well code. So the simpler I can make this, the better. That's why I liked the setInterval approach because nothing additional would be required of them. But if it noticeably slows down the site, I might have to take the other approach.

You should consider even delegation.
You just add one event listener to the document root and check the class of the element the event originated from (event.target). If you want to include also clicks from descendants, you'd have to traverse the DOM up form the target and check whether any of the ancestors contains the class.
I see two main advantages:
It works for newly generated elements without any extra steps (so the other developers don't have to do anything special).
It adds only one event handler instead of potentially many, which saves memory.
Disadvantages:
If other event handlers are registered along the path and they prevent the event from bubbling up, you cannot register this event.
A bit more information:
An event handler gets an event object as first argument. This object has several properties, among others, which element the event originated form.
E.g. to get the target element:
var element = event.target || event.srcElement;
This will be a DOM element and you can access the classes via element.className.
So your event listener could look like this (note that IE uses another method to attach event listeners and the event object is not passed but available via window.event):
function handler(event) {
event = event || window.event;
var target = event.target || event.srcElement;
if(target.className.match(/tracking\[[a-zA-Z0-9\.\-_]+\]/g) {
// do your stuff
}
}
if(document.addEventListener) {
document.addEventListener('click', handler, false);
}
else {
document.attachEvent('onclick', handler);
}
But as I said, this would miss events that are prevented from bubbling up. At least in the browsers following the W3C model (so not IE), you can handle the events in the capture phase by setting the last parameter to true:
document.addEventListener('click', handler, true);

If you can live without IE, then there is a change event which you can hook into for the window/document/dom element. Simply hook into the event at the document level, and it'd fire anytime something's changed in the page (stuff inserted, deleted, changed). I believe the event's context contains what got changed, so it should be fairly trivial to find any new trackable elements and attach your spy code to it.

A third option would be to write a method for manipulating the innerHTML of an element. At the end of that method simply call your function that refreshes everything.
example:
var setHtml = function(element, newHtml){
element.innerhtml = newHtml;
yourRefreshFunction();
}
So obviously this requires that you have your web developers user this method to update the dom. And you'll have to do it for anything that is more complicated than simple html edits. But that gives you the idea.
Hope that helps!