Added "Advanced Guides" page about cross-origin Errros

docs/docs/cross-origin-errors.md

@@ -0,0 +1,33 @@
+---
+id: cross-origin-errors
+title: Cross-origin Errors
+permalink: docs/cross-origin-errors.html
+---
+
+> Note:
+>
+> The following section applies only to the development mode of React. Error handling in production mode is done with regular try/catch statements.
+
+In [development mode](https://facebook.github.io/react/docs/optimizing-performance.html), React uses a global `error` event handler to preserve the "pause on exceptions" behavior of browser DevTools. It also logs errors to the developer console.
+
+If an error is thrown from a [different origin](https://developer.mozilla.org/en-US/docs/Web/Security/Same-origin_policy) the browser will mask its details and React will not be able to log the original error message. This is a security precaution taken by browsers to avoid leaking sensitive information.
+
+You can simplify the development/debugging process by ensuring that errors are thrown with a same-origin policy. Below are some common causes of cross-origin errors and ways to address them.
+
+### CDN
+
+When loading React (or other libraries that might throw errors) from a CDN, add the [`crossorigin`](https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_settings_attributes) attribute to your `<script>` tags:
+
+```html
+<script crossorigin src="..."></script>
+```
+
+Also ensure the CDN responds with the `Access-Control-Allow-Origin: *` HTTP header:
+
+![Access-Control-Allow-Origin: *](/react/img/docs/cdn-cors-header.png)
+
+### Webpack
+
+Some JavaScript bundlers may wrap the application code with `eval` statements in development. (For example Webpack will do this if [`devtool`](https://webpack.js.org/configuration/devtool/) is set to any value containing the word "eval".) This may cause errors to be treated as cross-origin.
+
+If you use Webpack, we recommend using the `cheap-module-source-map` setting in development to avoid this problem.