wappalyzer/src/drivers/webextension/js/inject.js

(() => {
  try {
    const detectJs = (chain) => {
      const properties = chain.split('.');

      let value = properties.length ? window : null;

      for (let i = 0; i < properties.length; i++) {
        const property = properties[i];

        if (value && value.hasOwnProperty(property)) {
          value = value[property];
        } else {
          value = null;

          break;
        }
      }

      return typeof value === 'string' || typeof value === 'number' ? value : !!value;
    };

    const onMessage = (event) => {
      if (event.data.id !== 'patterns') {
        return;
      }

      removeEventListener('message', onMessage);

      const patterns = event.data.patterns || {};

      const js = {};

      for (const appName in patterns) {
        if (patterns.hasOwnProperty(appName)) {
          js[appName] = {};

          for (const chain in patterns[appName]) {
            if (patterns[appName].hasOwnProperty(chain)) {
              js[appName][chain] = {};

              for (const index in patterns[appName][chain]) {
                const value = detectJs(chain);

                if (value && patterns[appName][chain].hasOwnProperty(index)) {
                  js[appName][chain][index] = value;
                }
              }
            }
          }
        }
      }

      postMessage({ id: 'js', js }, '*');
    };

    addEventListener('message', onMessage);
  } catch (e) {
    // Fail quietly
  }
})();