Why is document.execCommand("paste") not working in Google Chrome?

There used to be an experimental clipboard API in Chrome, but this was removed in Chrome 13.

Chrome has moved towards the more standard document.execCommand('paste'), document.execCommand('copy') and document.execCommand('cut') commands: https://developer.mozilla.org/en/Rich-Text_Editing_in_Mozilla#Executing%5FCommands

In Chrome you'll need permissions need to be added to your manifest: "clipboardRead" and "clipboardWrite". http://developer.chrome.com/extensions/declare_permissions.html

Up until Chrome 38, these clipboard permissions were only available to extension pages such as background scripts. As of Chrome 39, content scripts can also use these clipboard APIs after declaring the clipboard permissions in the manifest file (crbug.com/395376).

Calling document.execCommand("paste") is not supported by "reasonable" browsers, because of security concerns as it might enable the script to read sensitive data (like passwords) from the clipboard.

This is the compatibility matrix of document.execCommand("...") concerning clipboard events:

My two cents to this:

• The behaviour of Edge, Firefox and Chrome is "reasonable" as they prevent pasting/reading data from the clipboard. They do enable cut, as cut is simply a copy followed by a delete.
• The behaviour of IE makes no sense to me, as it enables the "risky" paste, but does not execute the cut event.

You can feature detect the possible commands using the document.queryCommandSupported method.

Edit: According to MDN document.queryCommandSupported is now deprecated and should no longer be used.

This works well for me in a background page.

function getClipboard() {
    var pasteTarget = document.createElement("div");
    pasteTarget.contentEditable = true;
    var actElem = document.activeElement.appendChild(pasteTarget).parentNode;
    pasteTarget.focus();
    document.execCommand("Paste", null, null);
    var paste = pasteTarget.innerText;
    actElem.removeChild(pasteTarget);
    return paste;
};

Of course your extension still needs "clipboardRead" permission and you have to use message passing to get this information back to your content script:

content.js:

chrome.extension.sendMessage({
    cmd: "clipboard", //$NON-NLS-0$
    action: "paste" //$NON-NLS-0$
}, function(response) {
    if (response.paste) {
        var range = document.getSelection().getRangeAt(0);
        range.deleteContents();
        range.insertNode(document.createTextNode(response.paste));
    }
});

background.js:

function getClipboard() {
    var pasteTarget = document.createElement("div");
    pasteTarget.contentEditable = true;
    var actElem = document.activeElement.appendChild(pasteTarget).parentNode;
    pasteTarget.focus();
    document.execCommand("Paste", null, null);
    var paste = pasteTarget.innerText;
    actElem.removeChild(pasteTarget);
    return paste;
};

function onClipboardMessage(request, sender, sendResponse) {
    if (request.action === "paste") { //$NON-NLS-0$
        sendResponse({
            paste: getClipboard()
        });
    }
}

chrome.extension.onMessage.addListener(onClipboardMessage);