Problem
I am making a Chrome extension that downloads files and adds links to these downloaded files to a webpage. When these links are clicked, I would like to relay the click as a "user gesture" to my background script so that the file opens without prompting. Looking at the docs on the relevant method, chrome.downloads.open, there is no discussion of user gestures.
Essentially, I want to get rid of this =>
using the idea in this comment.
Background
It seems like this is possible because
This post on what constitutes a user gesture lists click as one of the types of user gestures
The spec, which says clicks will generate a user gesture
In the code below, logging the event results in a MouseEvent, with type click and isTrusted set to true.
[downloads.open] can only run in a code initiated by a user action, like a click on a button. It cannot be executed from non-user events. - Xan, comment for How to open a downloaded file?
Code below aims to be an MCVE.
Content Script
// Add an event listener for every download link
function addDownloadListeners() {
const pathElems = document.getElementsByClassName('pathClass');
for (path of pathElems) {
path.addEventListener('click', openDownload);
}
}
// Send a message with the download ID to the background script
function openDownload(event) {
const selector = '#' + event.currentTarget.id;
const downloadId = parseInt($(selector).attr('download_id'));
chrome.runtime.sendMessage({
'downloadId': downloadId,
}, function(response) {
if (response !== undefined) {
resolve(response.response);
} else {
reject(new Error(response.response));
}
});
}
manifest.json
{
"background": {
"scripts": ["js/background.js"]
},
"content_scripts": [
{
"js": [
"js/content_script.js"
],
"matches": ["*://*.website.com/*/urlpath*"],
"run_at": "document_end"
}
],
"permissions": [
"downloads",
"downloads.open"
],
"manifest_version": 2,
}
Background Script
chrome.runtime.onMessage.addListener(
function(request, sender, sendResponse) {
try {
chrome.downloads.open(request.downloadId);
} catch (e) {
sendResponse({response: 'Error opening file with download id ' +
request.downloadId + ' getting error ' + e.toString()
});
}
}
)
Question
How can I get a click to open a download without creating an additional prompt?
This is not possible
It is not possible to prevent/use an alternative to prompts for chrome methods that require user consent. Based on this discussion in the Chromium Extension google group,
Some Chrome methods (like chrome.downloads.open) need to get user consent via prompt.
These are automatically generated via Chrome itself - they cannot be overridden or modified.
User gestures outside of prompts are not relevant to methods that require user consent.
This current behavior is circa 2014 for chrome.downloads.open.
Special thanks to #wOxxOm and Decklin Johnston for making this answer possible.
I am trying to trigger a block of code every time the user selects/highlights some text on any of the tabs.
I am able to run the javascript when I highlight some text and then click on my extension.
I have already read some of the chrome apis but none of them seem to work.
https://developer.chrome.com/extensions/api_index
chrome.browserAction.onClicked.addListener(function() {
alert(window.getSelection().toString());
});
I am not able to run the code as soon as I highlight some text. Is there an API that already handles that?
You should just add a buffer:
Store selection
As you are talking about selections from any tab, You should use the storage api and refer the tab id for further use.
document.onmouseup = function() {
chrome.tabs.getCurrent(function(_tabId){
if(_tabId){
var _SELECTION = {};
_SELECTION[tabId] = window.getSelection().toString();
chrome.storage.local.set(_SELECTION, function() {
console.log('Selection saved: ', _SELECTION[tabId]);
});
}
});
}
Use it when you click on your extension
chrome.browserAction.onClicked.addListener(function() {
chrome.tabs.getCurrent(function(_tabId){
if(_tabId){
chrome.storage.local.get(_tabId, function(result) {
alert('Selection restored: ' + result[tabId].txt);
});
}
});
});
Manifest
Don't forget to update your manifest.json to set the according permissions
{
...
"permissions": [
"storage",
"tabs"
],
...
}
Note
I used storage.local as the clipboard should be kept on the local machine, but if you want to share it cross-machines you can use storage.sync. More to read in the docs.
I'd use contextMenus. It makes more sense if you highlight text to right-click and perform an action.
I am trying to change the background of about:newtab in Firefox using the new WebExtensions API. At the moment, I don't understand why I receive the following error message in the debug console:
Unchecked lastError value: Error: No window matching {"matchesHost":[]}
The code for my add-on is as follows:
manifest.json
{
"background": {
"scripts": ["background.js"]
},
"description": "Yourdomain description.",
"homepage_url": "https://yourdomain.com",
"icons": {
"64": "icons/icon-64.png"
},
"manifest_version": 2,
"name": "yourDomain",
"permissions": [
"tabs",
"activeTab"
],
"version": "2.0"
}
background.js:
var tabId;
function changeBackground() {
chrome.tabs.insertCSS( tabId, {
code: "body { border: 20px dotted pink; }"
});
}
function handleCreated(tab) {
if (tab.url == "about:newtab") {
console.log(tab);
tabId = tab.id;
changeBackground();
}
}
chrome.tabs.onCreated.addListener(handleCreated);
Currently no way for WebExtensions add-ons to change about:newtab
That is the error you receive when the page into which you are attempting to inject does not match the match pattern, or can not be expressed as a match pattern (i.e. the URL must be able to be expressed as a match pattern, even if you didn't supply a match pattern). Match patterns must have a scheme that is one of http, https, file, ftp, or app. The error you are seeing is a result of not checking the runtime.lastError value in the callback function in tabs.insertCSS() when the error is the one expected when you attempt to inject code or CSS into an about:* page.
The MDN documentation is quite specific about not being able to use tabs.insertCSS() with any of the about:* pages (emphasis mine):
You can only inject CSS into pages whose URL can be expressed using a match pattern: meaning, its scheme must be one of "http", "https", "file", "ftp". This means that you can't inject CSS into any of the browser's built-in pages, such as about:debugging, about:addons, or the page that opens when you open a new empty tab [about:newtab].
Future:
Chrome has the manifest.json key chrome_url_overrides which allows overriding any of: bookmarks, history, or newtab. It appears that Firefox support for this manifest.json key is a "maybe".
Alternatives:
It is possible to override the newtab page with other types of Firefox add-ons.
You can use WebExtensions to detect that a tab has changed its URL to about:newtab and redirect the tab to a page of your choice.
Using tabs.insertCSS() or tabs.executeScript() for tabs, generally
If you are using tabs.insertCSS() or tabs.executeScript() in a situation where the tab normally contains a regular URL, but might be an about*: (or chrome:* scheme on Chrome) (e.g. a browser_action button), you could handle the error with the following code (tested and working in both Firefox WebExtensions and Chrome):
function handleExecuteScriptAndInsertCSSErrors(tabId){
if(chrome.runtime.lastError){
let message = chrome.runtime.lastError.message;
let isFirefox = window.InstallTrigger?true:false;
let extraMessage = tabId ? 'in tab ' + tabId + '.' : 'on this page.';
if((!isFirefox && message.indexOf('Cannot access a chrome:') > -1) //Chrome
||(isFirefox && message.indexOf('No window matching') > -1) //Firefox
){
//The current tab is one into which we are not allowed to inject scripts.
// You should consider alternatives for informing the user that your extension
// does not work on a particular page/URL/tab.
// For example: For browser_actions, you should listen to chrome.tabs events
// and use use browserAction.disable()/enable() when the URL of the
// active tab is, or is not, one for which your add-on can operate.
// Alternately, you could use a page_action button.
//In other words, using a console.log() here in a released add-on is not a good
// idea, but works for examples/testing.
console.log('This extension, ' + chrome.runtime.id
+ ', does not work ' + extraMessage);
} else {
// Report the error
if(isFirefox){
//In Firefox, runtime.lastError is an Error Object including a stack trace.
console.error(chrome.runtime.lastError);
}else{
console.error(message);
}
}
}
}
You could then change your changeBackground() code to:
function changeBackground(tabId) {
chrome.tabs.insertCSS( tabId, {
code: "body { border: 20px dotted pink; }"
}, handleExecuteScriptAndInsertCSSErrors.bind(null,tabId));
}
Obviously, changing your code like that won't actually allow you to change the background on the about:newtab page.
I am in the process of building a Chrome extension, and for the whole thing to work the way I would like it to, I need an external JavaScript script to be able to detect if a user has my extension installed.
For example: A user installs my plugin, then goes to a website with my script on it. The website detects that my extension is installed and updates the page accordingly.
Is this possible?
Chrome now has the ability to send messages from the website to the extension.
So in the extension background.js (content.js will not work) add something like:
chrome.runtime.onMessageExternal.addListener(
function(request, sender, sendResponse) {
if (request) {
if (request.message) {
if (request.message == "version") {
sendResponse({version: 1.0});
}
}
}
return true;
});
This will then let you make a call from the website:
var hasExtension = false;
chrome.runtime.sendMessage(extensionId, { message: "version" },
function (reply) {
if (reply) {
if (reply.version) {
if (reply.version >= requiredVersion) {
hasExtension = true;
}
}
}
else {
hasExtension = false;
}
});
You can then check the hasExtension variable. The only drawback is the call is asynchronous, so you have to work around that somehow.
Edit:
As mentioned below, you'll need to add an entry to the manifest.json listing the domains that can message your addon. Eg:
"externally_connectable": {
"matches": ["*://localhost/*", "*://your.domain.com/*"]
},
2021 Update:
chrome.runtime.sendMessage will throw the following exception in console if the extension isn't installed or it's disabled.
Unchecked runtime.lastError: Could not establish connection. Receiving end does not exist
To fix this, add this validation inside the sendMessage callback
if (chrome.runtime.lastError) {
// handle error
}
I am sure there is a direct way (calling functions on your extension directly, or by using the JS classes for extensions), but an indirect method (until something better comes along):
Have your Chrome extension look for a specific DIV or other element on your page, with a very specific ID.
For example:
<div id="ExtensionCheck_JamesEggersAwesomeExtension"></div>
Do a getElementById and set the innerHTML to the version number of your extension or something. You can then read the contents of that client-side.
Again though, you should use a direct method if there is one available.
EDIT: Direct method found!!
Use the connection methods found here: https://developer.chrome.com/extensions/extension#global-events
Untested, but you should be able to do...
var myPort=chrome.extension.connect('yourextensionid_qwerqweroijwefoijwef', some_object_to_send_on_connect);
Another method is to expose a web-accessible resource, though this will allow any website to test if your extension is installed.
Suppose your extension's ID is aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, and you add a file (say, a transparent pixel image) as test.png in your extension's files.
Then, you expose this file to the web pages with web_accessible_resources manifest key:
"web_accessible_resources": [
"test.png"
],
In your web page, you can try to load this file by its full URL (in an <img> tag, via XHR, or in any other way):
chrome-extension://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/test.png
If the file loads, then the extension is installed. If there's an error while loading this file, then the extension is not installed.
// Code from https://groups.google.com/a/chromium.org/d/msg/chromium-extensions/8ArcsWMBaM4/2GKwVOZm1qMJ
function detectExtension(extensionId, callback) {
var img;
img = new Image();
img.src = "chrome-extension://" + extensionId + "/test.png";
img.onload = function() {
callback(true);
};
img.onerror = function() {
callback(false);
};
}
Of note: if there is an error while loading this file, said network stack error will appear in the console with no possibility to silence it. When Chromecast used this method, it caused quite a bit of controversy because of this; with the eventual very ugly solution of simply blacklisting very specific errors from Dev Tools altogether by the Chrome team.
Important note: this method will not work in Firefox WebExtensions. Web-accessible resources inherently expose the extension to fingerprinting, since the URL is predictable by knowing the ID. Firefox decided to close that hole by assigning an instance-specific random URL to web accessible resources:
The files will then be available using a URL like:
moz-extension://<random-UUID>/<path/to/resource>
This UUID is randomly generated for every browser instance and is not your extension's ID. This prevents websites from fingerprinting the extensions a user has installed.
However, while the extension can use runtime.getURL() to obtain this address, you can't hard-code it in your website.
I thought I would share my research on this.
I needed to be able to detect if a specific extension was installed for some file:/// links to work.
I came across this article here
This explained a method of getting the manifest.json of an extension.
I adjusted the code a bit and came up with:
function Ext_Detect_NotInstalled(ExtName, ExtID) {
console.log(ExtName + ' Not Installed');
if (divAnnounce.innerHTML != '')
divAnnounce.innerHTML = divAnnounce.innerHTML + "<BR>"
divAnnounce.innerHTML = divAnnounce.innerHTML + 'Page needs ' + ExtName + ' Extension -- to intall the LocalLinks extension click here';
}
function Ext_Detect_Installed(ExtName, ExtID) {
console.log(ExtName + ' Installed');
}
var Ext_Detect = function (ExtName, ExtID) {
var s = document.createElement('script');
s.onload = function () { Ext_Detect_Installed(ExtName, ExtID); };
s.onerror = function () { Ext_Detect_NotInstalled(ExtName, ExtID); };
s.src = 'chrome-extension://' + ExtID + '/manifest.json';
document.body.appendChild(s);
}
var is_chrome = navigator.userAgent.toLowerCase().indexOf('chrome') > -1;
if (is_chrome == true) {
window.onload = function () { Ext_Detect('LocalLinks', 'jllpkdkcdjndhggodimiphkghogcpida'); };
}
With this you should be able to use Ext_Detect(ExtensionName,ExtensionID) to detect the installation of any number of extensions.
Another possible solution if you own the website is to use inline installation.
if (chrome.app.isInstalled) {
// extension is installed.
}
I know this an old question but this way was introduced in Chrome 15 and so I thought Id list it for anyone only now looking for an answer.
Here is an other modern approach:
const checkExtension = (id, src, callback) => {
let e = new Image()
e.src = 'chrome-extension://'+ id +'/'+ src
e.onload = () => callback(1), e.onerror = () => callback(0)
}
// "src" must be included to "web_accessible_resources" in manifest.json
checkExtension('gighmmpiobklfepjocnamgkkbiglidom', 'icons/icon24.png', (ok) => {
console.log('AdBlock: %s', ok ? 'installed' : 'not installed')
})
checkExtension('bhlhnicpbhignbdhedgjhgdocnmhomnp', 'images/checkmark-icon.png', (ok) => {
console.log('ColorZilla: %s', ok ? 'installed' : 'not installed')
})
I used the cookie method:
In my manifest.js file I included a content script that only runs on my site:
"content_scripts": [
{
"matches": [
"*://*.mysite.co/*"
],
"js": ["js/mysite.js"],
"run_at": "document_idle"
}
],
in my js/mysite.js I have one line:
document.cookie = "extension_downloaded=True";
and in my index.html page I look for that cookie.
if (document.cookie.indexOf('extension_downloaded') != -1){
document.getElementById('install-btn').style.display = 'none';
}
You could have the extension set a cookie and have your websites JavaScript check if that cookie is present and update accordingly. This and probably most other methods mentioned here could of course be cirvumvented by the user, unless you try and have the extension create custom cookies depending on timestamps etc, and have your application analyze them server side to see if it really is a user with the extension or someone pretending to have it by modifying his cookies.
There's another method shown at this Google Groups post. In short, you could try detecting whether the extension icon loads successfully. This may be helpful if the extension you're checking for isn't your own.
Webpage interacts with extension through background script.
manifest.json:
"background": {
"scripts": ["background.js"],
"persistent": true
},
"externally_connectable": {
"matches": ["*://(domain.ext)/*"]
},
background.js:
chrome.runtime.onMessageExternal.addListener(function(msg, sender, sendResponse) {
if ((msg.action == "id") && (msg.value == id))
{
sendResponse({id : id});
}
});
page.html:
<script>
var id = "some_ext_id";
chrome.runtime.sendMessage(id, {action: "id", value : id}, function(response) {
if(response && (response.id == id)) //extension installed
{
console.log(response);
}
else //extension not installed
{
console.log("Please consider installig extension");
}
});
</script>
Your extension could interact with the website (e.g. changing variables) and your website could detect this.
But there should be a better way to do this. I wonder how Google is doing it on their extension gallery (already installed applications are marked).
Edit:
The gallery use the chrome.management.get function. Example:
chrome.management.get("mblbciejcodpealifnhfjbdlkedplodp", function(a){console.log(a);});
But you can only access the method from pages with the right permissions.
A lot of the answers here so far are Chrome only or incur an HTTP overhead penalty. The solution that we are using is a little different:
1. Add a new object to the manifest content_scripts list like so:
{
"matches": ["https://www.yoursite.com/*"],
"js": [
"install_notifier.js"
],
"run_at": "document_idle"
}
This will allow the code in install_notifier.js to run on that site (if you didn't already have permissions there).
2. Send a message to every site in the manifest key above.
Add something like this to install_notifier.js (note that this is using a closure to keep the variables from being global, but that's not strictly necessary):
// Dispatch a message to every URL that's in the manifest to say that the extension is
// installed. This allows webpages to take action based on the presence of the
// extension and its version. This is only allowed for a small whitelist of
// domains defined in the manifest.
(function () {
let currentVersion = chrome.runtime.getManifest().version;
window.postMessage({
sender: "my-extension",
message_name: "version",
message: currentVersion
}, "*");
})();
Your message could say anything, but it's useful to send the version so you know what you're dealing with. Then...
3. On your website, listen for that message.
Add this to your website somewhere:
window.addEventListener("message", function (event) {
if (event.source == window &&
event.data.sender &&
event.data.sender === "my-extension" &&
event.data.message_name &&
event.data.message_name === "version") {
console.log("Got the message");
}
});
This works in Firefox and Chrome, and doesn't incur HTTP overhead or manipulate the page.
You could also use a cross-browser method what I have used.
Uses the concept of adding a div.
in your content script (whenever the script loads, it should do this)
if ((window.location.href).includes('*myurl/urlregex*')) {
$('html').addClass('ifextension');
}
in your website you assert something like,
if (!($('html').hasClass('ifextension')){}
And throw appropriate message.
If you have control over the Chrome extension, you can try what I did:
// Inside Chrome extension
var div = document.createElement('div');
div.setAttribute('id', 'myapp-extension-installed-div');
document.getElementsByTagName('body')[0].appendChild(div);
And then:
// On web page that needs to detect extension
if ($('#myapp-extension-installed-div').length) {
}
It feels a little hacky, but I couldn't get the other methods to work, and I worry about Chrome changing its API here. It's doubtful this method will stop working any time soon.
If you're trying to detect any extension from any website,
This post helped: https://ide.hey.network/post/5c3b6c7aa7af38479accc0c7
Basically, the solution would be to simply try to get a specific file (manifest.json or an image) from the extension by specifying its path. Here's what I used. Definitely working:
const imgExists = function(_f, _cb) {
const __i = new Image();
__i.onload = function() {
if (typeof _cb === 'function') {
_cb(true);
}
}
__i.onerror = function() {
if (typeof _cb === 'function') {
_cb(false);
}
}
__i.src = _f;
__i = null;
});
try {
imgExists("chrome-extension://${CHROME_XT_ID}/xt_content/assets/logo.png", function(_test) {
console.log(_test ? 'chrome extension installed !' : 'chrome extension not installed..');
ifrm.xt_chrome = _test;
// use that information
});
} catch (e) {
console.log('ERROR', e)
}
Here is how you can detect a specific Extension installed and show a warning message.
First you need to open the manifest file of the extension by going to chrome-extension://extension_id_here_hkdppipefbchgpohn/manifest.json and look for any file name within "web_accessible_resources" section.
<div class="chromewarning" style="display:none">
<script type="text/javascript">
$.get("chrome-extension://extension_id_here_hkdppipefbchgpohn/filename_found_in_ web_accessible_resources.png").done(function () {
$(".chromewarning").show();
}).fail(function () {
// alert("failed.");
});
</script>
<p>We have detected a browser extension that conflicts with learning modules in this course.</p>
</div>
Chrome Extension Manifest v3:
const isFirefox = chrome.runtime.OnInstalledReason.CHROME_UPDATE != "chrome_update";
For FireFox, I believe chrome.runtime.OnInstalledReason.BROWSER_UPDATE will be "browser_update": https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/OnInstalledReason
I'm toying around with Chrome trying to create my first extension. Basically, I want to create a script that does some DOM manipulation on a particular domain. Furthermore, I want the user to be able to toggle the script through an icon displayed in the address bar, when visiting that particular domain.
So far, I've got this manifest.json:
{
"manifest_version": 2,
"name": "Ekstrafri",
"description": "Removes annoying boxes for paid articles.",
"version": "1.0",
"page_action": {
"default_title": "Foobar"
},
"content_scripts": [
{
"matches": ["http://ekstrabladet.dk/*"],
"js": ["jquery.min.js", "cleaner.js"],
"run_at": "document_end"
}
]
}
cleaner.js contains a couple of jQuery DOM selectors that removes some stuff.
The current setup works, but the context script is injected all the time. I want the user to be able to toggle, which should trigger a confirmation prompt in which the user accepts or rejects a page reload.
Anyway, page_action doesn't seem to display any icon. According to the documentation, it should display an icon in the address bar.
I have two questions:
How do I display this page_action icon on the matched content?
How do I bind an event to that icon?
One thing you could do here is get and set a variable in a background.js page using the message passing framework. Essentially when the content-script runs you can contact the background script to check the state of a boolean variable. You can then determine whether or not to execute the rest of the script.
chrome.extension.sendMessage({ cmd: "runScript" }, function (response) {
if (response == true) {
//Run the rest of your script inside here...
}
});
You would also use this initial call to bind some UI on the page so you can toggle this state (i.e. switch the content script on/off). In this example I'm using a checkbox.
$("chkOnOff").click(function(){
var scriptOn = ($(this).is(":checked");
chrome.extension.sendMessage({ cmd: "updateRunScriptState", data: { "scriptOn" : scriptOn } }, function (response) {
//Update confirmed
});
});
The background.js page would look something like this:
//Global variable in background.js
var scriptOn = true;
chrome.extension.onMessage.addListener(
function (request, sender, sendResponse) {
if (request.cmd == "runScript") {
sendResponse(scriptOn);
}
if (request.cmd == "updateRunScriptState") {
//here we can update the state
scriptOn = request.data.scriptOn;
}
});
And don't forget to register the background.js page in the manifest.
..
"background": {
"scripts" : ["background.js"]
},
..