Load Raven async

raven.js

(function (global, document, url) {
  var calls = [];
  var spy = {};

  var methods = ['config', 'install', 'setUserContext', 'captureException'];
  for (var i = 0, method; method = methods[i]; i += 1) {
    spy[method] = (function (name) {
      return function () {
        calls.push([name, arguments]);
        return this;
      };
    }(method));
  }

  var define = Object.defineProperty;
  define(global, 'Raven', {
    get: function () { return spy },
    set: function (Raven) {
      global.removeEventListener('error', captureUnhandledExceptions);
      for (var i = 0, exception; exception = unhandledExceptions[i]; i += 1) {
        calls.push(['captureException', exception]);
      }

      define(global, 'Raven', {
        value: Raven,
        writable: true,
        enumerable: true,
        configurable: true,
      });

      for (var i = 0, call; call = calls[i]; i += 1) {
        Raven[call[0]].apply(Raven, call[1]);
      }
    },
    enumerable: true,
    configurable: true,
  });

  var unhandledExceptions = [];
  function captureUnhandledExceptions(event) {
    unhandledExceptions.push([
      event.error || new Error(event.message), {
        extra: {
          file: event.filename,
          line: event.lineno,
          column: event.colno
        }
      }
    ]);
  }

  global.addEventListener('error', captureUnhandledExceptions);

  global.addEventListener('load', function () {
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.crossOrigin = 'anonymous';
    script.async = true;
    script.src = url;

    var firstScript = document.getElementsByTagName('script')[0];
    firstScript.parentNode.insertBefore(script, firstScript);
  });
}(window, document, 'https://cdn.ravenjs.com/3.9.1/raven.min.js'));

@kl0tl, I found this from getsentry/sentry-javascript#169. Thanks for sharing it!

I have a question regarding this part:

spy[method] = (function (name) {
  return function () {
    calls.push([name, arguments]);
    return this;
  };
}(method));

What does the immediately invoked function provide? Essentially, I'm wondering if this can be replaced by:

spy[method] = function () {
  calls.push([method, arguments]);
  return this;
};

It seems that this will be the spy in either case. Is there something I'm missing?