Loading raven.js without blocking onload event

raven.lazy.js

/**
 * Setup Js error lazy tracking
 * - Pros: doesn't block rendering, onload event
 * - Cons: lower quality error reports for lazy errors
 *
 * @author vinhlh
 *
 * @param  {object} window
 * @param  {object} labJs
 * @param  {string} ravenCdn
 * @param  {string} sentryDsn
 */
(function(window, labJs, ravenCdn, sentryDsn) {
  var errors = [];
  var oldOnError = window.onerror;

  window.onerror = function() {
    errors.push(arguments);
    oldOnError && oldOnError.apply(this, arguments);
  };
  window.addEventListener('load', function() {
    labJs
      .script(ravenCdn)
      .wait(function() {
        window.onerror = oldOnError;
        Raven.config(sentryDsn).install();
        errors.forEach(function(args) {
          window.onerror.apply(this, args);
        });
      });
  });
})(window, $LAB, 'raven.min.js', 'https://xxx@sentry.io/9');