Script printed in Wordpress Metabox?

I'm seeing a script being printed in each text metabox on my WordPress site:

if (
  (function rt() {
    return (
      !!window.Ember ||
      !!window.Vue ||
      !!window.Meteor ||
      !(!window.React && !document.querySelector("[data-reactroot], [data-reactid]")) ||
      !!(
        window.angular ||
        document.querySelector(".ng-binding, [ng-app], [data-ng-app], [ng-controller], [data-ng-controller], [ng-repeat], [data-ng-repeat]") ||
        document.querySelector('script[src*="angular.js"], script[src*="angular.min.js"]')
      )
    );
  })()
) {
  window.postMessage({ singlePageAppCheck: true });
} else {
  window.postMessage({ singlePageAppCheck: false });
}

I'm not sure what it is or where it came from, and I can't really read it - does this look familiar to anyone, or is this a hack?