Chrome Extension (MV3): Read Google Tag Manager dataLayer

background.js

chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
  (async () => {
    const { action } = request;
    const { tab } = sender;

    // Get global value(s) from main frame
    if (action === 'get-datalayer') {
      const injectionResults = await chrome.scripting.executeScript({
        target: { tabId: tab.id },
        func: () => window.dataLayer,
        world: 'MAIN',
      });

      sendResponse(injectionResults[0].result);
    }
  })();

  // Return true to indicate an async response
  return true;
});

content.js

(async () => {
  // If necessary, await document.readyState, document.visibilityState, etc.
  
  const response = await browser.runtime.sendMessage({
    action: 'get-datalayer',
  });

  console.log('content received a response:', response);
})();

manifest.json

{
  "permissions": ["activeTab", "scripting"]
}