Pass data from chrome extension to webpage

Question

I am able to pass data from my webpage to chrome extension. My code goes as follows.

var id = "myExtensionId";
    chrome.runtime.sendMessage(id, { messageFromWeb: "Sample message" }, function (response) {
});

I am able to get the tab Id at the extension side. But how can I send back data from the extension to the tab? Is the following code correct?

chrome.runtime.onMessageExternal.addListener(
    function(request, sender, sendResponse) {
        if (request.messageFromWeb) {
            console.log(request.messageFromWeb);
        }

        chrome.tabs.sendMessage(sender.tab.id,{ greeting: "hello" });
    }
);

The code, chrome.tabs.sendMessage(sender.tab.id,{ greeting: "hello" }); does not throw error. How should be listening at the web page to get events from extension?

Answer 1

From content script to website script

Because the content script and the scripts in the website can see the same DOM, you can use it to communicate between them. Is as easy as:

Content script:

// data you want to sent
var data = {
    random: 'Some data',
    more: 'More data'
};

// send data through a DOM event
document.dispatchEvent(new CustomEvent('csEvent', {detail: data}));

Website script:

// Listen you CRX event
document.addEventListener('csEvent', function (event) {
    var data = event.detail;

    // Do something with you data from CRX
});

---

From content script to background script

How to do it depends on which type of connection you need: one-time or long-lived. From Chrome Developer page Messaging:

There is a simple API for one-time requests and a more complex API that allows you to have long-lived connections for exchanging multiple messages with a shared context.

If you only want to send a response back, here is an example:

chrome.runtime.onMessage.addListener(
    function(request, sender, sendResponse) {
        console.log(sender.tab ?
                "from a content script:" + sender.tab.url :
                "from the extension");

        sendResponse({farewell: "Message back!"});
    });

Edited to add content script to website script way