Loading html into page element (chrome extension)

URL of a file inside an extenion folder has the following format:

chrome-extension://<ID>/topbar.html

You can get this path by running:

chrome.extension.getURL("topbar.html")

Now if you try to do:

$('#topbar').load(chrome.extension.getURL("topbar.html"));

it wouldn’t let you because of cross-origin policy. Background pages don’t have this limitation, so you would need to load HTML there and pass result to a content script:

content_script.js:

chrome.extension.sendRequest({cmd: "read_file"}, function(html){
    $("#topbar").html(html);
});

background.html:

chrome.extension.onRequest.addListener(function(request, sender, sendResponse) {
    if(request.cmd == "read_file") {
        $.ajax({
            url: chrome.extension.getURL("topbar.html"),
            dataType: "html",
            success: sendResponse
        });
    }
})

In a real world you probably would read topbar.html only once and then reuse it.