I am forced to use a web application written (over a decade ago I'm guessing) for IE6 and only works with IE (newer versions in quirks mode). I have been able to repair some of the more egregious javascript with a Safari extension that injects scripts to detach event handlers and replace them with DOM compliant versions.
I am now turning my attention to annoyances rather than the downright broken. The heavy handed use of alerts to inform the user of progress is painful. I thought it would be a fairly nice addition to my extension to override the window.alert function with some css popovers, but the challenge I am having is with pages that are sent back after an http post, where the first thing they do is display a success (or failure) alert.
According to this Apple documentation "a Start Script executes when the document has been created but before the webpage has been parsed". I would have thought that if the page hadn't been parsed, the scripts in the page's body's script tags wouldn't run, but this is not the behaviour I am seeing. Instead, it appears that any scripts in the page returned from the post response execute before my start script even loads.
To test this I have a very simple start script that logs to the console location.href and tries to replace window.alert with console.log.
The injected start script:
console.log(window.location.href + "loaded killAlert.js") ;
window.alert=function(str) { console.log(str) ; }
The test web page:
<html><head></head>
<body>
<script>alert("this is an alert message") ;</script>
nothing to see here... move along.
</body>
</html>
What happens is that when loading a test page with a script embedded, the alert executes before anything is written to console.log.
My questions—
When do start scripts actually get called?
Is there any way I can get them to execute before any scripts on the page?
While this seems like it should be fairly straight forward, but so far I haven't been able to find a way around the problem through reading documentation, search or experimenting. I'm hoping someone else has solved something similar.
<head>
<script>
(function() {
console.log(window.location.href + "loaded killAlert.js") ;
window.alert=function(str) { console.log(str) ; }
})();
</script>
</head>
Try calling it anonymously, it will execute the script immediately after the creation. Hope it helps.
Related
When executing a jquery $.get() call to retrieve an html file that includes a script tag with a src attribute, I am getting the warning "Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience." in Firefox's console. Here is some simple code that I used to narrow down the warning that demonstrates this:
foo.html
<html>
<head>
<script src="http://code.jquery.com/jquery-1.11.2.js"></script>
</head>
<body>
<script>$.get("bar.html", function(data) { $('#testdiv').html(data);});</script>
<div id="testdiv"></div>
</body>
</html>
bar.html
<script src="foo.js"></script>
Note that foo.js is empty, so nothing in there seems to be causing the warning. I don't understand the reason for this. Would anybody know what's causing this?
I started to wholly investigate this issue myself and the warning is being generated by your browser when JQuery dynamically loads a page that contains a script tag with a reference to an external script.
So, in your case, foo.html loads bar.html and as your browser begins to parse the content from bar.html it encounters <script src="foo.js"></script> which causes the browser to stop parsing content, load and execute foo.js. If you don't have any code in foo.js, you won't notice any detriments to performance, but if your browser takes any discernible amount of time to parse and execute foo.js then your end user will actually lose control of the browser (meaning the browser will appear to be frozen) until foo.js finishes executing. This is what is meant by the warning's message: detrimental effects to the end user's experience.
The work around that I am considering is to implement custom events to trigger the relevant pieces of my code at the proper time which is probably a better idea to begin with. I am curious to know if anyone else has any clever ways of circumventing the issue.
I'm trying to create a Firefox extension that fires my Javascript code before any of the current page's Javascript is fired. My Javascript code will basically control whether or not the page's Javascript code can be executed or denied.
I first started out by trying to follow this answer, but I couldn't really figure out how to get it to work and realized I was relying on onDOMContentLoaded, which loads after the Javascript has already executed.
I then turned my attention toward XPCOM, but once again didn't really understand what the Firefox tutorials were telling me.
I've recently been trying to make an extension through Firebug, but I seem to hit the same problem... only having access to the Javascript after it's been parsed/executed. Here's the resulting code that I wrote. I think if I could access the file's objects in the onExamineResponse event, my problem could be solved, but I don't know how to do that... I'm talking about this code:
BeepbopListener.prototype = {
onRequest: function(context, file) {
...
},
onExamineResponse: function(context, file) {
FBTrace.sysout("onexamineresponse " + file); // this returns something like
// '[xpconnect wrapped (nsISupports, nsIHttpChannel, nsIRequest, nsIUploadChannel, nsITraceableChannel, nsIHttpChannelInternal)]'
// but I don't know how to access those elements...
var pattern = /\.js$/;
if (pattern.test(file.href) && FBTrace.DBG_BEEPBOP) {
FBTrace.sysout("ONEXAMINE DOESN'T EVEN GET IN THIS IF SO YOU WON'T SEE THIS");
}
},
...
};
So my question is... is there a tutorial out there that shows me how I can get access to all Javascript code on a page before it's executed? Also, if anyone has any helpful insight, I'd love to hear it. Oh, and if y'all need more code from me, just let me know, and I'll post it.
You can access a new document before any JavaScript code runs by listening to the content-document-global-created observer notification. However, the document will be empty at this point and JavaScript code will run as soon as the parser adds a <script> tag - you cannot really prevent it. Here are the options to control script execution that I am aware of.
1) Disable all JavaScript for a window using nsIDocShell.allowJavascript:
wnd.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
.getInterface(Components.interfaces.nsIWebNavigation)
.QueryInterface(Components.interfaces.nsIDocShell)
.allowJavascript = false;
This is an all or nothing approach. Note that JavaScript stays disabled even when a new document loads into the same frame.
2) Implement the nsIContentPolicy interface in an XPCOM component and register it in the content-policy category (via nsICategoryManager). Your shouldLoad() function will be able to block scripts selectively - but it will only called for external scripts (meaning <script src="...">), not for inline scripts on the page.
3) Use JavaScript debugger service to intercept script execution. You could use jsdIDebuggerService.interruptHook to step through JavaScript execution and abort the script whenever you like. But that would slow down JavaScript execution very significantly of course. At the very least you should use jsdIDebuggerService.addFilter() to restrict it to a particular document, otherwise you will slow down the entire browser (including browser UI).
I'm trying to create a Firefox extension that fires my Javascript code before any of the current page's Javascript is fired. My Javascript code will basically control whether or not the page's Javascript code can be executed or denied.
Start by completely preventing the document from getting parsed altogether then on the side, fetch the same document, do any processing on this document and then inject the resulting document in the page. Here is how I currently do just that https://stackoverflow.com/a/36097573/6085033
I have a script that I want to be injected into the document BEFORE load. I.E; it should function as if
<script..>MYSCRIPT HERE</script>
<html>
.
.
I have made a script in chrome that executes correctly (I can alert(0) etc) but, it runs in different environment which is not what I want. I want it to run in the SAME environment as page.
Earlier, I had used a trick where in the startup script I had used
window.location="javascript:<MY SCRIPT HERE>"
which effectively changes the execution environment but for the past few days it isn't working. I think its a chrome bug fix. Is there any other workaround for this? Note: I can't add script tags dynamically to the page in the startup script because the document.body etc are unavailable.
I would like to provide you more details of why I need this and my previous solution.
HTML Page which I don't have control over:
.
.
<script>
function a(){//DOSOMETHING}
</script>
.
.
<script>
a(); <<------ I DONT WANT TO CALL THIS
</script>
Solution: startup JavaScript contains
window.location='javascript:const a=function(){};';<<-CONST used!!
That will force error of re-declaration of 'a' when the page actually loads, hence, when a() is called, nothing happens. (clever, right? -_-)
But now, I realized when I do window.location="js:..", even that runs in separate env!
You should be able to inject script into the page's JavaScript context by adding a script tag via your content script. In other words, your script could be injected at document_idle, and execute something like:
var s = document.createElement('script');
s.textContent = 'const a = function () {};';
document.documentElement.appendChild(s);
That script tag would be executed in the context of the page, not in the context of your script, and should allow you to achieve the result you're looking for.
Documentation for content scripts in general is available at https://developer.chrome.com/extensions/content_scripts
Chrome probably has a bug in the current build as PAEz pointed out. But yes, a lot of insight on how things can be injected into "document" using chrome extension. Thanks Mike for the post. Will keep that in mind the next time I'm injecting using greesemonkey or something :)
I ask because I'm running an application in which I load an external script file in the HEAD section of the page, and then attempt to call a function from it in the onLoad section of the BODY tag.
external.js
function someFunction()
{
alert("Some message");
}
myPage.html
<html>
<head>
<script type="text/javascript" language="javascript" src="external.js"></script>
</head>
<body onLoad="someFunction();">
</body>
</html>
Using the developer tools in IE8, I get an exception thrown at the onLoad statement because, apparently, the external javascript file hasn't been loaded yet.
I haven't had this problem come up in IE7 before, thus my question.
Did they change the load order between IE7 and IE8? If so, is there a better way to do this? (the real function references many other functions and constants, which look much better in an external file)
Thanks,
B.J.
Well, I feel pretty stupid actually.
Turns out the problem wasn't with the load order. The problem was that the external javascript file had a syntax error in one of its functions, and apparently when the exception was thrown it completely invalidated the whole file, thus making the rest of the functions unavailable to the main page.
I'm not sure if this behavior is different in IE8 compared to IE7, but anyway, that was the real problem.
Thanks for your reply.
B.J.
I doubt very much that his has changed it would break a considerable number of websites.
Try this (without using the developer tools):-
<body onload="alert(somefunction)">
this shouldn't break and will tell you whether at the point onload executes whether the identifier somefunction can be seen.
Assuming that what you think is happening is what is happening, you should try to attach the body.onLoad later on.
To simplify things, you can do it with Prototype (including prototype, of course) with
Event.observe(window, 'load', function() { myFunction.init() });
or JQuery (including JQuery) with
$(document).ready(function(){
// Your code here...
});
I think there is a pure Javascript way to do this, but the problem is that the body element won't exist yet, so it's rough...
That said, I have had no problems running body onload in Javascript with IE8, and putting it right into the body tag, using external files. I'm going to test that right now out of curiosity, and I'll report back.
Edit: There's no problem doing the onload from an external file. However, while we're at it, you might want to get to know JQuery, Prototype or Scriptaculous :)
I have an ASP.NET MVC project that uses some simple AJAX functionality through jQuery's $.get method like so:
$.get(myUrl, null, function(result) {
$('#myselector').html(result);
});
The amount of content is relatively low here -- usually a single div with a short blurb of text. Sometimes, however, I am also injecting some javascript into the page. At some point when I dynamically include script into content that was itself dynamically added to the page, the script still runs, but it ceases to be available to the debugger. In VS2008, any breakpoints are ignored, and when I use the "debugger" statement, I get a messagebox saying that "no source code is available at this location." This fails both for the VS2008 debugger and the Firebug debugger in Firefox. I have tried both including the script inline in my dynamic content and also referencing a separate js file from this dynamic content -- both ways seemed to result in script that's unavailable to the debugger.
So, my question is twofold:
Is there any way to help the debugger recognize the existence of this script?
If not, what's the best way to include scripts that are used infrequently and in dynamically generated content in a way that is accessible to the debuggers?
I can not comment yet, but I can maybe help answer. As qwerty said, firefox console can be the way to go. I'd recommend going full bar and getting firebug. It hasn't ever missed code in my 3 years using it.
You could also change the way the injected javascript is added and see if that effects the debugger you're using. (I take it you're using Microsoft's IDE?).
In any case, I find the best way to inject javascript for IE is to put it as an appendChild in the head. In the case that isn't viable, the eval function (I hate using it as much as you do) can be used. Here is my AJAX IE fixer code I use. I use it for safari too since it has similar behavior. If you need that too just change the browser condition check (document.all for IE, Safari is navigator.userAgent.toLowerCase() == 'safari';).
function execajaxscripts(obj){
if(document.all){
var scripts = obj.getElementsByTagName('script');
for(var i=0; i<scripts.length; i++){
eval(scripts[i].innerHTML);
}
}
}
I've never used jquery, I preferred prototype then dojo but... I take it that it would look something like this:
$.get(myUrl, null, function(result) {
$('#myselector').html(result);
execajaxscripts(result);
});
The one problem is, eval debug errors may not be caught since it creates another instance of the interpreter. But it is worth trying.. and otherwise. Use a different debugger :D
This might be a long shot, but I don't have access to IE right now to test.
Try naming the anonymous function, e.g.:
$.get(myUrl, null, function anon_temp1(result) {
$('#myselector').html(result);
});
I'm surprised firebug is not catching the 'debugger' statement. I've never had any problems no matter how complicated the JS including method was
If this is javascript embedded within dynmically generated HTML, I can see where that might be a problem since the debugger would not see it in the initial load. I am surprised that you could put it into a seperate .js file and the debugger still failed to see the function.
It seems you could define a function in a seperate static file, nominally "get_and_show" (or whatever, possibly nested in a namespace of sorts) with a parameter of myUrl, and then call the function from the HTML. Why won't that trip the breakpoint (did you try something like this -- the question is unclear as to whether the reference to the .js in the dynamic HTML was just a func call, or the actual script/load reference as well)? Be sure to first load the external script file from a "hard coded" reference in the HTML file? (view source on roboprogs.com/index.html -- loads .js files, then runs a text insertion func)
We use firebug for debug javascript, profile requests, throw logs, etc.
You can download from http://getfirebug.com/
If firebug don't show your javascript source, post some url to test your example case.
I hope I've been of any help!
If you add // # sourceURL=foo.js to the end of the script that you're injecting then it should show up in the list of scripts in firebug and webkit inspector.
jQuery could be patched to do this automatically, but the ticket was rejected.
Here's a related question: Is possible to debug dynamic loading JavaScript by some debugger like WebKit, FireBug or IE8 Developer Tool?