CODE EXAMPLE FOR JAVASCRIPT

chrome extension sendmessage await until getdata

// waiting for tasks from background
chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
    const item = msg.item;

    // Asynchronously process your "item", but DON'T return the promise
    asyncOperation().then(() => {
      // telling that CS has finished its job
      sendResponse({complete: true});
    });

    // return true from the event listener to indicate you wish to send a response asynchronously
    // (this will keep the message channel open to the other end until sendResponse is called).
    return true;
});