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executing javascript through url

I'm trying to set the value of a textarea on the following page by executing something similar the below javascript:
javascript:alert(document.getElementsByClassName('uiTextareaNoResize uiTextareaAutogrow _1rv DOMControl_placeholder')[0].value='blabla');
This works if I manually enter the code into the address bar on the target page, but I want to pass this argument through a link.. ie...
<a href="/nextpage.php?javascript:alert(document.getElementsByClassName('uiTextareaNoResize uiTextareaAutogrow _1rv DOMControl_placeholder')[0].value='blabla');"
Just wondered if anything like this is possible at all?

You can send the arguments via the url like you would for GET requests. Then have the receiving page parse location.search.
For instance, you can send it like this:
http://example.com/?arg1=foo&arg2=bar
And the receiving page have a script like this:
var queryString = location.search; //?arg1=foo&arg2=bar
You'll have to parse it manually though, removing the ?, split by & then each by =

This is called XSS or Cross-Site-Scripting, and as many comments have already pointed out, it is a security issue. This is why most major browsers do NOT allow it.
However, I believe that some browsers do allow it, for example Opera - although I can't recall exactly which version.
If you are looking to make your own "browser", I would recommend using C# .Net WebBrowser, then use the runtime package XULRunner (https://developer.mozilla.org/en-US/docs/Mozilla/Projects/XULRunner).
Despite all this, I would not recommend doing anything that may be against laws of your current location, or doing anything to displease the site owner.

Javascript and Flash in AS3

Is it possible to use Javascript in flash. For example, as a simple test I am trying to use Javascript's alert method when a button is clicked.
I am using AS3. Is it possible?

Like Marty mentioned, you can use the ExternalInterface class to execute a Javascript. Your options are to execute a function embedded in the (html) page code and create one from scratch. Because alert is a default function you can use its name as the first parameter for the call method (of ExternalInterface) and the string as the 2nd one.
If you provide a single parameter, you might wanna write a function instead to execute (or return) something.
btn.addEventListener(MouseEvent.CLICK, btnClicked);
function btnClicked(e:MouseEvent):void {
ExternalInterface.call("alert","something");
// or
ExternalInterface.call("function(){alert('something');}");
}

No.. Flash uses ActionScript 3.
You can call a JavaScript function on the same page as an embedded SWF using ActionScript's ExternalInterface class, though.
A quick demo on implementing ExternalInterface:
if(ExternalInterface.available)
ExternalInterface.call("alert", "Hello!");
Tip: ExternalInterface calls will not work locally unless you add the location of the project in this security settings panel and check "always allow".

Silverlight 4 MVVM: Call Javascript function from viewmodel

we have developed an Intranet Management Application with Silverlight 4. We have been asked to add the functionality to call a remote desktop tool which is installed on clients using the Intranet SL App. In an earlier version of the tool written in ASP.NET we just added a Javascript function to the aspx page like this:
function RunShellCommand()
{
var launcher = new ActiveXObject("WScript.Shell");
launcher.Run("mstsc.exe");
}
and called it from ASP.NET.
Now it's clear that SL4 is running in a sandbox and that I cant use the AutomationFactory to create a WScript.Shell object (out of browser mode is not an option).
I thought I could circle around the problem by, again, adding the RunShellCommand javascript method in the aspx page where the SL4 control is hosted and call it via
HtmlPage.RegisterScriptableObject("Page", this);
HtmlPage.Window.Invoke("RunShellCommand", "dummydata");
from my ViewModel. When I run the Application the debugger just skips the RegisterScriptableObject method and quits. Nothing happens.
My question is if am doing something wrong or if this just wont work this way.
Is it possible that I cant do a RegisterScriptableObject from a viewmodel?
EDIT: When I explicitly put a try, catch block around the two methods I get an ArgumentException from the first method stating that the current instance has no scriptable members. When I delete the first method and only run the Invoke, I get a browser error stating that the automation server cant create the object. So is there really no way (except OOB mode) to do this?

Yes, the explanation is correct: you should add at least one method with the ScriptableMember attribute in order that you can use the RegisterScriptableObjectmethod. But it is used only for calling C#-methods from JavaScript.
As far as I see, you want to do the opposite: to call JavaScript code from the Silverlight application. Then you need only one line:
HtmlPage.Window.Invoke("RunShellCommand");
The error automation server cant create the object has nothing to do with Silverlight. I'm sure that if you call the JS function directly - the error will remain.
According to the internet, the reason might be not installed Microsoft Windows Script. Or it is because of security restrictions of the browser.

Crawling and parsing Javascript elements

I try to get info from a website which uses Javascript to show onclick the phonenumber of the items/companies.
Crawling that with PHP curl or xpath did not let me find a solution how to trigger this events and than keep on crawling.
Example:
<a onclick="show(2423,'../entries.php?eid=2423',1);
for info here the function too
function show(info_id,qpath,swimage){
expandit(info_id,0,swimage);
if(document.getElementById('load_'+info_id)) {
ajax_loadContent('cont_td_'+info_id,qpath);
}
}
Is this possible to do with PHP/Xpath/DOM or what do you recommend to do to achieve this?
Any chance for "debugging" the code to see which url to call?
THanks for your concern
And have really great FESTIVITIES

It seems like all it's doing is an AJAX call to this page, ../entries.php?eid=2423.
Try going to that URL directly and you'll probably get your phone number without any HTML/JavaScript parsing.

You could use the net tab of firebug to keep an eye on what URLs are loaded. Or Fiddler. Once you work out the pattern you might be able to craft and call the same URLs yourself using curl.
Or, you could use one of the browser automation frameworks, like webaii or selenium or watir or watin and crawl the links that way.

Try using Selenium RC to simulate clicking on the link and then scan the page for results:
http://seleniumhq.org/projects/remote-control/

Calling a flash external interface AS3 function on page load

I have a function defined in AS3 that's gonna be called from client side via JavaScript. The AS3 functions simply print some value on SWF screen when it's called.
It works fine when I set an onclick event handler to a button and call the AS3 function. However I want to call this AS3 function as soon as the page loads. I am using jQuery in the project and I placed the call to the AS3 function inside $(document).ready(), but that gives me the following error in FF2 firebug:
getFlashMovie("my_movie_name").my_as3_function is not a function
Then, I tried calling the by setting an onLoad event handler on the , but that also does not work - produces the same error.
So, my question is, how do I call an AS3 function automatically once page loads? In my project, I need to pass some client side initialization information to the flash once page loads.

You'll need to have your flash call a function in the page to notify it that the Flash is loaded and initialized, then use that as your entrypoint.
In the flash:
ExternalInterface.call('flashReady');
In the page:
<script>
function flashReady() {
..
}
</script>

If you use swfObject to embed your SWF (probably a good idea anyway) then you can use its addDomLoadEvent() function which allows you to do something once the SWF is fully loaded
swfobject.addDomLoadEvent(function() {
$("#swfobject").get(0).inited('you are loaded!');
});

i am not trying to be a wiseguy here but do you test your work on a server?
external interface, addcallback dose not work on local filesystem, and eventually you may have to add:
flash.system.Security.allowDomain('http://localhost');
if you are running on local.
:P

The problem is that the Flash object is not initialized yet when the page finishes loading. It would probably be much safer to perform this initialization from within AS3. If you want to pass values from the HTML page, use flashVars.

I ran into this problem myself a couple of weeks ago. The solution is pretty simple :)
First, you need to put in your DOM a div
<div id="timewriter"><div>
You'll also be using the jQuery Timers plugin to time your loading. After this preparation the things will go very easy.
The following piece of code will go in your $(document).ready();
var movie = getFlashMovie('my_movie_name');
if(movie.PercentLoaded() != 100)
{
$("#timewriter").everyTime(100, function ()
{
if(movie.PercentLoaded() == 100)
{
$("#timewriter").stopTime();
//the movie is loaded, call here your functions; usually this happens if you don't use cache
}
});
}
else
{
//the movie is loaded, call here your functions; usually you get here if you use cache
}
Later edit: be careful that HTML page load doesn't mean the swf was loaded, that happens right after the web page load complete event. Also my solution is based on jQuery javascript library.

Answers by both tweakt and Bogdan are viable. Use tweakt's method if you have access to the Actionscript. Use Bogdan's if you don't. I was looking for an alternative besides polling (when you don't have access to the Actionscript) but I have been unsuccessful in finding one thus far. Events are mentioned here: http://www.adobe.com/support/flash/publishexport/scriptingwithflash/scriptingwithflash_03.html But noone seems to know how to use them.

For the sake of completion, you would also have to use import flash.external.*; to make everything work.

It seems like the collection of answers offered answers this closest to it's entirety.
As David Hanak said, the flash object cannot be accessed yet because it is initializing, though i disagree that we must rely on flashvars, though I love them.
Tweakt is right, but upon calling the function in the javascript, have that call the javascript function that calls back to your swf; This way we know flash is ready as it sent the first call.