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've integrated Sentry with my website a few days ago and I noticed that sometimes users receive this error in their console:
ChunkLoadError: Loading chunk <CHUNK_NAME> failed.
(error: <WEBSITE_PATH>/<CHUNK_NAME>-<CHUNK_HASH>.js)
So I investigated the issue around the web and discovered some similar cases, but related to missing chunks caused by release updates during a session or caching issues.
The main difference between these cases and mine is that the failed chunks are actually reachable from the browser, so the loading error does not depend on the after-release refresh of the chunk hashes but (I guess), from some network related issue.
This assumption is reinforced by this stat: around 90% of the devices involved are mobile.
Finally, I come to the question: Should I manage the issue in some way (e. g. retrying the chunk loading if failed) or it's better to simply ignore it and let the user refresh manually?
2021.09.28 edit:
A month later, the issue is still occurring but I have not received any report from users, also I'm constantly recording user sessions with Hotjar but nothing relevant has been noticed so far.
I recently had a chat with Sentry support that helped me excluding the network related hypotesis:
Our React SDK does not have offline cache by default, when an error is captured it will be sent at that point. If the app is not able to connect to Sentry to send the event, it will be discarded and the SDK will no try to send it again.
Rodolfo from Sentry
I can confirm that the issue is quite unusual, I share with you another interesting stat: the user affected since the first occurrence are 882 out of 332.227 unique visitors (~0,26%), but I noticed that the 90% of the occurrences are from iOS (not generic mobile devices as I noticed a month ago), so if I calculate the same proportion with iOS users (794 (90% of 882) out of 128.444) we are near to a 0,62%. Still small but definitely more relevant on iOS.
This is most likely happening because the browser is caching your app's main HTML file, like index.html which serves the webpack bundles and manifest.
First I would ensure your web server is sending the correct HTTP response headers to not cache the app's index.html file (let's assume it is called that). If you are using NGINX, you can set the appropriate headers like this:
location ~* ^.+.html$ {
add_header Cache-Control "no-store max-age=0";
}
This file should be relatively small in size for a SPA, so it is ok to not cache this as long as you are caching all of the other assets the app needs like the JS and CSS, etc. You should be using content hashes on your JS bundles to support cache busting on those. With this in place visits to your site should always include the latest version of index.html with the latest assets including the latest webpack manifest which records the chunk names.
If you want to handle the Chunk Load Errors you could set up something like this:
import { ErrorBoundary } from '#sentry/react'
const App = (children) => {
<ErrorBoundary
fallback={({ error, resetError }) => {
if (/ChunkLoadError/.test(error.name)) {
// If this happens during a release you can show a new version alert
return <NewVersionAlert />
// If you are certain the chunk is on your web server or CDN
// You can try reloading the page, but be careful of recursion
// In case the chunk really is not available
if (!localStorage.getItem('chunkErrorPageReloaded')) {
localStorage.setItem('chunkErrorPageReloaded', true)
window.location.reload()
}
}
return <ExceptionRedirect resetError={resetError} />
}}>
{children}
</ErrorBoundary>
}
If you do decide to reload the page I would present a message to the user beforehand.
The chunk is reachable doesn't mean the user's browser can parse it. For example, if the user's browser is old. But the chunk contains new syntax.
Webpack loads the chunk by jsonp. It insert <script> tag into <head>. If the js chunk file is downloaded but cannot parsed. A ChunkLoadError will be throw.
You can reproduce it by following these steps. Write an optional chain and don't compile it. Ensure it output to a chunk.
const obj = {};
obj.sub ??= {};
Open your app by chrome 79 or safari 13.0. The full error message looks like this:
SyntaxError: Unexpected token '?' // 13.js:2
MAX RELOADS REACHED // chunk-load-handler.js:24
ChunkLoadError: Loading chunk 13 failed. // trackConsoleError.js:25
(missing: http://example.com/13.js)
I have a webapp which has the domain http://draft.mo2do.com
when i am accessing the url it will resolve like the below url and redirect to the corresponding site home page
http://draft.mo2do.com/s/_91665/Home
Here i implemented offline cache. My cache.manifest file is the below
CACHE MANIFEST
# Offline cache v4.0
# All other resources (e.g. sites) require the user to be online.
NETWORK:
*
# Additional resources to cache CACHE:
# Add the pages in to the cache
/s/_91665/Home /s/_91665/CachedDraftBoard
http://draft.mo2do.com
# Add the images in to the cache
/s/store/-1/webapp/styles/webapp.css
/s/store/-1/webapp/styles/nba_draft.css
/s/store/-1/webapp/styles/add2drafthome.css?v2
# Add the js files in to the cache
/s/store/-1/webapp/scripts/jquery-1.5.min.js
/s/store/-1/webapp/scripts/iscroll.js
/s/store/-1/webapp/scripts/webapp.js
/s/store/-1/webapp/scripts/nba_draft.js
/s/store/-1/webapp/scripts/cacheUpdate.js
/s/store/-1/webapp/scripts/add2drafthome.js?v0.9.4
/webapp/icon.png /webapp/startup.png
/s/store/-1/webapp/nba/addtodrafthome/arrow.png
/s/store/-1/webapp/nba/addtodrafthome/close-bubble.png
/s/store/-1/webapp/nba/addtodrafthome/icon.png
/s/store/-1/webapp/nba/addtodrafthome/plus.png
/s/store/-1/webapp/nba/addtodrafthome/share.png
FALLBACK:
http://draft.mo2do.com
If i am directly accessing the site url the caching is working and that time i didnt mention the "http://draft.mo2do.com" in the cache section.During this time offline cache is working fine.
If i directly access only the domain url "http://draft.mo2do.com" in the browser it is not opening 404 in the offline mode.
Then i added the "http://draft.mo2do.com" in the cache section that time i am getting exception
Application Cache Progress event (2 of 3) http://draft.mo2do.com/ Application Cache Error event: Resource fetch failed (-1) http://draft.mo2do.com/
If i access the domain also it should load the app in the offline mode. If i access direct url app is loading fine.
How can I solve this issue?
The cache has to directly reference specific resources, be they Javascript, CSS, HTML pages, images, whatever. From what I can tell from the content above, you've done that. Simply placing a domain in there however won't work (you also need to reference all of the pages you want off-line, e.g. /s/_91665/Home needs to be in there).
So, there's an error somewhere along the line, but it's hard to figure out what you mean by this:
If i directly access only the domain url "http://draft.mo2do.com" in the browser it is not opening 404 in the offline mode.
Can you be more clear? Do you mean that going to that URL results in a 404, or is there something in the page itself that's in error?
Are you sure that your cache file is functioning as intended? If there are any errors at all in your cache file, your off-line application simply won't work. This page offers some debugging code which may help:
Debugging HTML 5 Offline Application Cache