Add hook to handleError.

Why:

* It is hard to send exceptions to an exception tracker (e.g. Rollbar)
  when they're all caught and sent to console.error.

This change addresses the need by:

* Update handleError to check for the existence of a logException
  function on the window, then pass the exception to it if it exists.

node_package/src/ReactOnRails.js

@@ -12,6 +12,7 @@ const ctx = context();
 
 const DEFAULT_OPTIONS = {
   traceTurbolinks: false,
+  exceptionLogger: function(e) {}
 };
 
 ctx.ReactOnRails = {
@@ -56,13 +57,19 @@ ctx.ReactOnRails = {
    * Set options for ReactOnRails, typically before you call ReactOnRails.register
    * Available Options:
    * `traceTurbolinks: true|false Gives you debugging messages on Turbolinks events
+   * `exceptionLogger: function Gets passed the exception as the first argument
    */
   setOptions(options) {
     if (options.hasOwnProperty('traceTurbolinks')) {
       this._options.traceTurbolinks = options.traceTurbolinks;
       delete options.traceTurbolinks;
     }
 
+    if (options.hasOwnProperty('exceptionLogger')) {
+      this._options.exceptionLogger = options.exceptionLogger;
+      delete options.exceptionLogger;
+    }
+
     if (Object.keys(options).length > 0) {
       throw new Error('Invalid options passed to ReactOnRails.options: ', JSON.stringify(options));
     }

node_package/src/handleError.js

@@ -63,4 +63,6 @@ ${e.stack}`;
     const reactElement = React.createElement('pre', null, msg);
     return ReactDOMServer.renderToString(reactElement);
   }
+
+  ReactOnRails.options('excptionLogger')(e);
 };

node_package/tests/ReactOnRails.test.js

@@ -42,6 +42,15 @@ test('ReactOnRails accepts traceTurbolinks as an option false', (assert) => {
   assert.equal(actual, false);
 });
 
+test('ReactOnRails accepts exceptionLogger as an option function', (assert) => {
+  ReactOnRails.resetOptions();
+  assert.plan(1);
+  const logger = function() {};
+  ReactOnRails.setOptions({ exceptionLogger: logger });
+  const actual = ReactOnRails.option('exceptionLogger');
+  assert.equal(actual, logger);
+});
+
 test('ReactOnRails not specified has traceTurbolinks as false', (assert) => {
   ReactOnRails.resetOptions();
   assert.plan(1);

spec/dummy/client/app/startup/clientRegistration.jsx

@@ -14,7 +14,10 @@ import CssModulesImagesFontsExample from '../components/CssModulesImagesFontsExa
 import SharedReduxStore from '../stores/SharedReduxStore'
 
 ReactOnRails.setOptions({
-  traceTurbolinks: true
+  traceTurbolinks: true,
+  exceptionLogger: function(e) {
+    console.log('Log from exceptionLogger:', e);
+  }
 });
 
 ReactOnRails.register({