executeScript.js

const code = `(function getUrls(){
  const forkUrl = document.querySelector('meta[name="octolytics-dimension-repository_parent_nwo"]') 
    ? document.querySelector('meta[name="octolytics-dimension-repository_parent_nwo"]').content
    : undefined;

  const url = document.querySelector('meta[name="go-import"]') 
    ? document.querySelector('meta[name="go-import"]').content.split(' ')[0]
    : undefined;

  const href = window.location.href;

  return { forkUrl, url, href };
})()`; 

chrome.tabs.executeScript(tabId, { code }, function(result) {
  const { forkUrl, url, href } = result[0];

  if (forkUrl) {
    document.getElementById("url").innerText = `
      git remote add upstream https://github.com/${forkUrl}
      git fetch upstream
      git branch --set-upstream-to=upstream/master master`;
  } else if (url) {
    document.getElementById("url").innerText = `
      git remote add upstream https://${url}
      git fetch upstream
      git branch --set-upstream-to=upstream/master master`;
  } else {
    document.getElementById("url").innerText = `
      git remote add upstream ${href}
      git fetch upstream
      git branch --set-upstream-to=upstream/master master`;
  }
});