Chrome extension : sendResponse returning empty object

Question

I know there are a lot of similar questions : Chrome extension messaging: sendResponse returning empty object, etc., but I read and tried all of them before asking my question. My problem is a bit different, so I think that's why their solutions don't work for me.

I want to detect Ctrl+C from the user, so when he clicks on extension icon, the content of the clipboard is displayed inside the popup.

Here's what I've done : a part of manifest.json :

 "permissions": [ "activeTab", "tabs", "<all_urls>", "clipboardRead" ], "content_scripts": [ { "matches": ["*://*/*"], "js": ["oncopy.js"] } ], "background": { "scripts": ["background.js"], "persistent": false }

oncopy.js (content script)

//https://stackoverflow.com/questions/2870369/google-chrome-extensions-how-to-detect-copy-action-ctrl-c-and-edit-copy function onCopy(e) { chrome.extension.sendMessage({event: "copy"}); } document.addEventListener('copy',onCopy,true);

background.js (background script) :

 var clipboardContents; // This part of the script receive the 'copy' event. chrome.extension.onMessage.addListener( function(request, sender, sendResponse) { if (request.event == "copy") { // #### GET CLIPBOARD CONTENT ################################################# bg = chrome.extension.getBackgroundPage(); // get the background page bg.document.body.innerHTML= ""; // clear the background page // add a DIV, contentEditable=true, to accept the paste action var helperdiv = bg.document.createElement("div"); document.body.appendChild(helperdiv); helperdiv.contentEditable = true; // focus the helper div's content helperdiv.innerHTML=""; // clear the buffer var range = document.createRange(); range.selectNode(helperdiv); window.getSelection().removeAllRanges(); window.getSelection().addRange(range); helperdiv.focus(); // trigger the paste action bg.document.execCommand("Paste"); clipboardContents = helperdiv.innerText; // ############################################################################ } sendResponse({}); }); function send_response(callback){ callback(clipboardContents); } chrome.runtime.onMessage.addListener(function(message,sender,sendResponse){ // When we get a message from the popup send_response(function(clipboardContents) { sendResponse(clipboardContents.toString()); }); return true; // I also tried sendResponse() only, wih and without the return true; // I also tried sendResponse(clipboardContents) only and sendResponse({data: clipboardContents}); });

popup.js :

 chrome.runtime.sendMessage('popup_opened',function(response){ document.getElementById('text').innerHTML = response; // I tried response.data });

I always get :
response = an empy object
response.toString() = "[Object : object]"
response.data = undefined

I don't understand what I'm doing wrong. I hope you can help, and that the answer has not be explained elsewhere yet.

woxxom · Accepted Answer · 2020-04-07 09:36:44Z

The actual cause of the problem is that extension.onMessage is a deprecated alias for runtime.onMessage so you have two listeners for the same event but only the first registered listener's sendResponse is transferred to the caller and that is {}.

That said, the entire workflow can be extremely simplified: there's no need for the background script or the content script so you can remove "background" and "content_scripts" from manifest.json. No need for messaging either.

You need a browser_action popup and simply read the clipboard in the popup script.

manifest.json:

{ "manifest_version": 2, "name": "test", "version": "1.0", "browser_action": { "default_popup": "popup.html" }, "permissions": [ "clipboardRead" ] }

popup.html:

<!DOCTYPE html> <body> <p id=text contenteditable=true></p> <script src=popup.js></script> </body>

popup.js:

document.getElementById('text').focus(); document.execCommand('paste');

This is the entire content of the extension.

Collectives™ on Stack Overflow

Chrome extension : sendResponse returning empty object

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related