angular/projects/shell-chrome/src/inject.ts

export const injectScripts = (scripts: string[], cb?: () => void) => {
  let injected = 0;
  scripts.forEach(s =>
    injectScript(chrome.runtime.getURL(s), () => {
      injected++;
      if (injected === scripts.length && cb) {
        cb();
      }
    })
  );
};

const injectScript = (scriptName: string, cb: () => void) => {
  const src = `
    (function() {
      var script = document.constructor.prototype.createElement.call(document, 'script');
      script.src = "${scriptName}";
      document.documentElement.appendChild(script);
      script.parentNode.removeChild(script);
    })()
  `;
  chrome.devtools.inspectedWindow.eval(src, (_, err) => {
    if (err) {
      console.log(err);
    }
    cb();
  });
};