How to dynamically send chrome extension ID to a webpage for message passing

Question

Im injecting a script in webpage via content script. Inside the script I am using chrome.runtime.sendMessage to successfully send a message to background script. However I have the extensionId hardcoded. How would I dynamically inject the extension id in webpage to send messages to background script?

chrome.runtime.sendMessage(extensionIdHardCoded, {
      msg: data
    },
    function(response) {});

Answer 1

First off, if you already have a content script, you don't have to use externally_connectable to communicate - you could use custom events to communicate with the content script that would forward it to background.

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That said, you can use chrome.runtime.id and pass it to the window context before injecting your script:

var script = document.createElement('script');
script.textContent = "var extensionId = " + JSON.stringify(chrome.runtime.id);
(document.head||document.documentElement).appendChild(script);
script.parentNode.removeChild(script);

/* now inject your script */

Alternatively, you could add an invisible DOM node that would contain the ID as content or some attribute and read that from the injected script.