I'm trying to display an image selected from the local machine and I need the location of that image for a JavaScript function. But I'm unable to get the location.
To get the image location, I tried using console.log, but nothing returns.
console.log(document.getElementById("uploadPreview"));
Here's the HTML code:
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<div align="center" style="padding-top: 50px">
<img align="center" id="uploadPreview" style="width: 100px; height: 100px;" />
</div>
<div align="center" style="padding-left: 30px">
<input id="uploadImage" type="file" name="myPhoto" onchange="PreviewImage();" />
</div>
<script type="text/javascript">
function PreviewImage() {
var oFReader = new FileReader();
oFReader.readAsDataURL(document.getElementById("uploadImage").files[0]);
oFReader.onload = function (oFREvent) {
document.getElementById("uploadPreview").src = oFREvent.target.result;
console.log(document.getElementById("uploadPreview").src);
};
}
</script>
</body>
</html>
Console Output:
Here's the warning:
DevTools failed to load SourceMap: Could not load content for
chrome-extension://alplpnakfeabeiebipdmaenpmbgknjce/include.preload.js.map:
HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
That's because Chrome added support for source maps.
Go to the developer tools (F12 in the browser), then select the three dots in the upper right corner, and go to Settings.
Then, look for Sources, and disable the options:
"Enable JavaScript source maps"
"Enable CSS source maps"
If you do that, that would get rid of the warnings. It has nothing to do with your code. Check the developer tools in other pages and you will see the same warning.
Go to Developer tools → Settings → Console → tick "Selected context only". The warnings will be hidden. You can see them again by unticking the same box.
The "Selected context only" means only the top, iframe, worker and extension contexts. Which is all that you'll need, the vast majority of the time.
Fixing "SourceMap" error messages in the Development Tools Console caused by Chrome extensions:
Examples caused by McAfee extensions:
DevTools failed to load SourceMap: Could not load content for chrome-extension://klekeajafkkpokaofllcadenjdckhinm/sourceMap/content.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
DevTools failed to load SourceMap: Could not load content for chrome-extension://fheoggkfdfchfphceeifdbepaooicaho/sourceMap/chrome/content.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
DevTools failed to load SourceMap: Could not load content for chrome-extension://fheoggkfdfchfphceeifdbepaooicaho/sourceMap/chrome/iframe_handler.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
If you are developing, then you need "Enable JavaScript source maps" and "Enable CSS source maps" checked to be able see your source code in Chrome Developer Tools. Unchecking those takes away your ability to debug your source code. It is like turning off the fire alarm instead of putting out the fire. You do not want to do that.
Instead you want to find the extensions that are causing the messages and turn them off. Here is how you do that:
Go to the three dots in the upper right hand corner of Chrome.
Go to "More Tools" and click on "Extensions".
Do this for one extension at a time until no more "SourceMap" errors are in the console:
Turn off the extension by sliding the switch to the left.
Reload the page that you were using the Development Tools on.
Check if any of the "SourceMap" error messages disappeared.
If any did, then that extension was causing those messages.
Otherwise, that extension can be turned back on.
After determining which extensions caused the issue either:
If you need it, then contact the maker to have them fix the issue.
Otherwise, remove the extension.
I stumbled upon this Stack Overflow question after discovering loads of source map errors in the console for the Edge browser. (I think I had disabled the warnings in the Chrome browser long ago.)
For me it meant first realising what a source map is; please refer to Macro Mazzon's answer to understand this. Since it's a good idea, it was just a case of finding out how to turn them on.
It's as simple as adding this line in your webpack.config.js file -
module.exports = {
devtool: "source-map",
}
Now that Edge could detect a source map, the errors disappeared.
Apologies if this answer insults anybody's intelligence, but maybe somebody reading this will be as clueless about source maps as I was.
The include.prepload.js file will have a line like below, probably as the last line:
//# sourceMappingURL=include.prepload.js.map
Delete it and the error will go away.
For me, the problem was caused not by the application in development itself, but by the Chrome extension React Developer Tool. I solved it partially by right-clicking the extension icon in the toolbar, clicking "Manage extension" and then enabling "Allow access to files URLs." But this measure fixed just some of the alerts.
I found issues in the React repository that suggests the cause is a bug in their extension and is planned to be corrected soon - see issues 20091 and 20075.
You can confirm is extension-related by accessing your application in an anonymous tab without any extension enabled.
Chrome has changed the UI in 2022, so this is a new version of the most upvoted reply.
Open the dev tools (hit F12 or Option + Command + J)
Select the gear at the top. There are two gears in that area, so be sure to select the one at the top, top.
Locate the Sources section
Deselect "Enable JavaScript source maps"
Check to see if it worked!
Right: it has nothing to do with your code. I've found two valid solutions to this warning (not just disabling it). To better understand what a source map is, I suggest you check out this answer, where it explains how it's something that helps you debug:
The .map files are for JavaScript and CSS (and now TypeScript too) files that have been minified. They are called SourceMaps. When you minify a file, like the angular.js file, it takes thousands of lines of pretty code and turns it into only a few lines of ugly code. Hopefully, when you are shipping your code to production, you are using the minified code instead of the full, unminified version. When your app is in production, and has an error, the sourcemap will help take your ugly file, and will allow you to see the original version of the code. If you didn't have the sourcemap, then any error would seem cryptic at best.
First solution: apparently, Mr Heelis was the closest one: you should add the .map file and there are some tools that help you with this problem (Grunt, Gulp and Google closure for example, quoting the answer). Otherwise you can download the .map file from official sites like Bootstrap, jQuery, font-awesome, preload and so on... (maybe installing things like popper or swiper by the npm command in a random folder and copying just the .map file in your JavaScript/CSS destination folder)
Second solution (the one I used): add the source files using a CDN (content delivery network). (Here are all the advantages of using a CDN). Using content delivery network (CDN) you can simply add the CDN link, instead of the path to your folder. You can find CNDs on official websites (Bootstrap, jquery, popper, etc.) or you can easily search on some websites like Cloudflare, cdnjs, etc.
Extensions without enough permissions on Chrome can cause these warnings, for example for React developer tools. Check if the following procedure solves your problem:
Right click on the extension icon.
Or
Go to extensions.
Click the three-dot in the row of React developer tool.
Then choose "This can read and write site data".
You should see three options in the list. Pick one that is strict enough based on how much you trust the extension and also satisfies the extension's needs.
I appreciate this is part of your extensions, but I see this message in all sorts of places these days, and I hate it: how I fixed it (this fix seems to massively speed up the browser too) was by adding a dead file
physically create the file it wants it/where it wants it, as a blank file (for example, "popper.min.js.map")
put this in the blank file
{
"version": 1,
"mappings": "",
"sources": [],
"names": [],
"file": "popper.min.js"
}
make sure that "file": "*******" in the content of the blank file matches the name of your file ******.map (minus the word ".map")
(I suspect you could physically add this dead file method to the addon yourself.)
I do not think the warnings you have received are related. I had the same warnings which turned out to be the Chrome extension React Dev Tools. I removed the extension and the errors were gone.
You have just missing files.
Go to the website https://www.cdnpkg.com/.
Download what you need and copy it to the right folder.
For me, the warnings were caused by the Selenium IDE Chrome extension. These warnings appeared in the Console on every page load:
DevTools failed to load source map: Could not load content for chrome-extension://mooikfkahbdckldjjndioackbalphokd/assets/atoms.js.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
DevTools failed to load source map: Could not load content for chrome-extension://mooikfkahbdckldjjndioackbalphokd/assets/polyfills.js.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
DevTools failed to load source map: Could not load content for chrome-extension://mooikfkahbdckldjjndioackbalphokd/assets/escape.js.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
DevTools failed to load source map: Could not load content for chrome-extension://mooikfkahbdckldjjndioackbalphokd/assets/playback.js.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
DevTools failed to load source map: Could not load content for chrome-extension://mooikfkahbdckldjjndioackbalphokd/assets/record.js.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME
Since Selenium IDE was already set to be able to read site data on all sites, I uninstalled it. (I read in another comment here that you might try enabling more permissions for an extension instead of removing it.) In my case, removing Selenium IDE (Chrome extension) got rid of the warnings.
It is also possible to add the file that is missing, aside with other .js libraries in the same folder (no need to reference the .map in the .html file, <script> tag).
I had the same error, when trying to code in Backbone.js.
The problematic file was backbone-min.js, and the line that created the error was sourceMappingURL=backbone-min.map.
After downloading the missing file (the link comes from here), the error disappeared.
I had the same problem. I tried to disable the extensions one by one to check it, and finally realized I had Adblock enabled, which was causing this issue. To remove that error I followed the step below,
Three dots (top right corner).
Click More tools --> extensions.
Disable the Adblock.
Reload the page.
And it should work now.
DevTools failed to load source map: Could not load content for chrome-extension://cfhdojbkjhnklbpkdaibdccddilifddb/browser-polyfill.js.map: System error: net::ERR_FILE_NOT_FOUND
Disable the Chrome extension "Adblock Plus - free ad blocker". https://chrome.google.com/webstore/detail/adblock-plus-free-ad-bloc/cfhdojbkjhnklbpkdaibdccddilifddb
Lately this error is caused by the extension.
Problems with Debugging and Sourcemaps in Web Browsers
Hope this clarifies the technicals behind the problem...knowing how things works helps some :)
This browser error means it has some compiled version of your JavaScript in a sourcemap intermediate file it or some 3rd party created that is now needed when debugging that same script in "devtools" in your web browser.
This can happen if your script fails (or in your case trying to get an image source hidden in the sourcemap code that created the script) but whose script error is tied to some JavaScript that got created from an original sourcemap file that now cannot be found to debug that same error. So it's an error about an error, a missing debugging file creating a new error. (crazy, huh?)
This error is likely coming from an extension in the web browser and is reporting it has generated a script error it has recorded in the console.log window of devtools (press F12 in the browser). The error is likely from the extension (not your code) saying it has some code that contains an address to a sourcemap file it cannot access, has a bad URI/URL address, is blocked, or that is missing.
The browser only needs this sourcemap file if a developer using devtools will need to debug the original script again.
A sourcemap, by the way, is a file that translates or transpiles code from one language to another language. Often this is a file that the browser uses to translate this source code into a child script like JavaScript/ECMAScript, or when it needs to do the opposite and recreate the source file from the child script. In most cases this file is not needed at all as a 3rd party software program has already compiled or transpiled the source code into the child script for the browser. For example, developers who like TypeScript use it to create JavaScript. This source code gets transpiled into JavaScript so the browser script engine can run it. The URI/URL to this sourcemap file is usually at the top of the javaScript or application compiled code file in a format like //#....
When this intermediary transpile file is missing or blocked for security reasons in a web browser, the application will usually not care unless it needs the source file for debugging the child script using this source file. In that case it will complain when it feels it needs this file and cannot find it, as it uses it to recreate the source file for the code running in the browser when debugging the script in order to allow a developer to debug the original source code. When it cannot find it, it means that any developer trying to debug it will not be able to do so, and is stuck with the compiled code only. So it is safe to turn off these errors in the various ways mentioned in this post. It should not affect your own scripts if it is connected to an extension. Even if it is related to your own scripts, it is still unlikely you need it unless you plan to run debugging from devtools.
In my case, it was JSON Viewer extension that was blocking the source map files from being loaded
In my case i made silly mistake by adding bootstrap.min.js instead of bootstrap.bundel.js :)
You need to open Chrome in developer mode: select More tools, then Extensions and select Developer mode
I know that to debug content script use normal web developer tools (https://developer.mozilla.org/en/docs/Mozilla/Add-ons/WebExtensions/Debugging#Debugging_content_scripts), and this works perfect. debugger keyword works as intended.
But in this exact situation things get broken:
addon.id = "123-568-485"; // I never define `addon` before this line, so this cause: ReferenceError: "addon is not defined". We aren't aware of this mistake.
// Some more code
// Some more code
// Some more code
// Some more code
debugger; // Here we want to stop execution and inspect, some other stuff. Remember that we aren't aware of earlier mistake.
What we would expect, that in console error about Reference error will appear, but it doesn't. Console get silent, and we don't know why our debugger keyword doesn't work.
This kind of silent error, happened to me when I misspell variable name. In result couldn't figure out what's wrong.
The errors in the content script are not reported in the tab's Web Console due to Firefox bug 1410932, which is not fixed (as of Firefox 79, released on 2020-07-28).
I listed possible workarounds in another answer:
use try..catch with logging,
check the Browser Console (which does show errors from the content script)
use the Debugger's "pause on exceptions" option.
Content scripts are executed in webpage, So as you know to see it's output you should open up console menu in that specific web page (ctrl+shift+e then go to console).
But if something is wrong with content script and cause it to throw exception, The error log would be shown in debug area of your extension in: about:debugging
I think the reason is content scripts are treated like extra frame for webpage and their error is shown there.
This question already has answers here:
Suppress Chrome 'Failed to load resource' messages in console
(3 answers)
Closed 5 years ago.
The Chrome Developer Tools console logs an error each time a page asset (including an image) isn't found (i.e. returns 404).
In my work, I'm often working on sites where images are provided by third parties and may not be available during development. Having each missing image show up as an error in the console makes other more important errors (e.g. JavaScript errors) harder to notice.
Is there a setting that stops the console logging unfound images as errors?
Or is there some way to filter console messages by the same sort of criteria that you can filter requests by in the Network tab?
(See e.g. http://chromium.googlecode.com/issues/attachment?aid=1337330000000&name=Screenshot-Google%2B+-+Google+Chrome.png&token=1F05er8uKjAQEEBrUITFjsIGJ2A%3A1358867878658&inline=1)
Work has "started" on this by the Chromium team: https://code.google.com/p/chromium/issues/detail?id=96212
Update: The feature request was closed on March 18, 2013. I'm not sure in which version of Chrome this feature first appeared, but I can confirm console filtering options in my Chrome v33.0.1750.152 (Linux).
Update 2: Currently, when a filter (plain text or regular expression) is entered, it is tested against the message text (e.g. GET http://example.com/foobar 404 (Not Found)) as well as the text of the right side link (e.g. test.html:65). (I have filed an issue with Chromium to track this.)
As a workaround, use a regular expression filter like:
^(?!.* 404 \(Not Found\))(?!.*[file name])
where [file name] is the file name from the right side link.
For example, if my page is test.html, then ^(?!.* 404 \(Not Found\))(?!.*test\.html) will work.
Note: This will also filter out messages that have the file name in the message text. I'm not sure there is a way around this for now.
Update (2019-06-05): This expression will filter out 404s in my current version of Chrome (75.0.3770.80):
-/404\s\(Not\sFound\)$/
It seems the filtering first splits the filter string by whitespace before processing each token, but it will also split spaces inside of a regular expression, so the \s's are necessary.
Technically, this will filter out any message ending with the (case insensitive) string "404 (Not Found)", including console.log messages.
In the chrome developer tools, it's under the "Console" tab. Click "Filter" and it will be on the filter line as a checkbox.
As an alternative answer you could run a bit of javascript to alter the src attribute of the offending images when on your dev server (just make sure you don't publish it to your production environment!).
If you don't want to actually add javascript to the page (understandably) you could probably run the script on load of the page via a chrome plugin (perhaps the greasemonkey chrome clone - tampermonkey).
n.b. Thanks for the feedback, notably for this to work it'll need to be within an event after the dom is ready and before the images load.
In your app, in your 'catch' statement.. log the exception under 'console.warn' .. know it works with firebug. In Firebug, you can then find these 'errors' under the 'warnings' tab. I would like to think the same can be true for Chrome Developer Tools..
actually did something similar day ago.. my app would stop on some error, so, I instead used the 'try' and 'catch' block. My catch looks like:
catch (e) {
console.warn(e);
}
I'm using IE9 to debug a web app. I made some changes to the javascript after loading the page. I'm not able to get IE9 to stop on the new code. The message is "The code in the document is not loaded". I can set breakpoints when I'm not debugging, but they won't be valid when I start debugging. I'm using IE7 Browswer Mode, IE7 Document Mode.
Things I've tried:
close dev tools window, re-open
stop debugging, start debugging
Ctrl R in dev tools window (same as Clear Browser Cache button)
Ctrl R on the IE9 web page
Ctrl F5 on the Ie9 web page
Clear browser cache for this domain
Check (set) Always refresh cache from server
Next thing to try (I guess) would be closing IE completely. Is that the fix for this? If so, yuck. It takes me a couple of minutes to set the page up so doing that after every JS change really stinks. I can use FF4 to develop the JS, but the JS issue I'm seeing is specific to IE7 so I have to do it this way.
>> How can I get IE9 (running in IE7 mode) to reliably debug the most current JS from the server?
This issue wasn't related to caching etc. IE9 was hitting a script error (missing closing paren) in the new code and not allowing breakpoints anywhere in the script. IE seemed very quiet about the script error though. Anyway, fixing the script error fixed the issues with breakpoints / caching.
If you have access to the code:
In you javascript file reference add a query string, something like this:
<script src="Scripts/main.js?v=1" type="text/javascript"></script>
And every time you change in the js file change the v value to something else, like that the browser will feel that this is a new file and will get it.
Add this:
window.applicationCache.addEventListener('updateready', function (e)
{
if (window.applicationCache.status == window.applicationCache.UPDATEREADY)
{
window.applicationCache.swapCache();
if (confirm('A new version of this site is available. Load it?'))
window.location.reload();
}
}, false);
I found this solution somwhere in the Net. Sorry, but I don't remember the author. It works for me when I debug Web App with JavaScript in Visual Studio and use IE.
I found this question based on the "the code in the document is not loaded" error message. I'm not using IE7 document mode or any of that, just IE9.
Like jcollum, my issue wasn't related to caching.
I'm using MVC.Net, and someone had set up a piece of javascript to rely on a string in the ViewBag. I changed a couple things, and that ViewBag string disappeared, so the resulting javascript looked something like this:
if(!()) {
// Some code
}
Javascript died right here, and wouldn't process the rest of the code in the block. This was confusing, as it was still trying to execute javascript in a different set of script tags, but which relied on a variable set in the other block it wouldn't load.
So, basically, a syntax error was introduced via strange means, and the debugger refused to load some of the code which came after it. Another lesson on the dangers of ViewBag.
I'm working on some old AJAX code, written in the dark dark days before jQuery. Strangely, it has been working fine for years, until today when it suddenly stopped firing its callback. Here's the basic code:
var xml = new XMLHttpRequest(); // only needs to support Firefox
xml.open("GET", myRequestURL, true);
xml.onreadystatechange = function() { alert ('test'); };
xml.send(null);
Checking the Firebug console, the request is being sent with no worries, and it is receiving the correct XML from the request URL, but the onreadystatechange function is not working at all. There's no javascript errors or anything else strange happening in the system.
I wish I could just rewrite everything using jQuery, but I don't have the time right now. What could possibly be causing this problem??
A further update - I've been able to test my code in a different browser (FFx 3.0) and it was working there, so it must be a problem with my browser. I'm running Firefox 3.5b4 on Vista, and I've tried it now with all my addons disabled with no luck. It's still really bugging me because I was working on this site yesterday (with the same browser setup) and there were no problems at all...
Actually I just took a look back in my Addons window and saw that Firebug was still enabled. If I disable Firebug, it works perfectly. If I enable it, it's broken. Firebug version 1.40.a31
is the url malformed?
have you tried putting the whole thing in a try-catch and alerting the errors (if any)
is it failing on an authorization check?
does the url in question require http-auth? (though there should be state changes in this case, I'll admit)
edit:
I have a really funny thought here. Are you using firefox 3.5 beta4? I develop a firefox extension for a browser-based game and recently discovered some odd behvaviour. With my extension or firebug observing the ajax requests made from the page, the script ccreating them would never get calledback. The request would be correctly observed and processed by both firebug and my extension (I could observe what was sent and received)... but the page itself would never hear from the request again -- like it had disappeared into a black hole.
Try turning off firebug (or at least turn off listening to 'Net' for that domain) and test it again
Known Firefox bug affecting Firebug; see http://code.google.com/p/fbug/issues/detail?id=1569&q=xhr&colspec=ID%20Type%20Status%20Owner%20Test%20Summary for details :-)
It seems unlikely that onreadystatechange would stop working. Is it possible that the 'alert' function has somehow been disabled or overridden? Can you replace the alert with some code to make a visible change in the page, and check its functionality that way? (I know, its a stretch, but it just seems so strange that onreadystatechange wouldn't work!)