Why is IE8 getting a script error when using Facebook's React.js

Make sure to add the polyfills listed at the end of this page:Refs and the DOM

Note also that JSXTransformer.js is currently incompatible with IE8, so you do need to precompile your JSX.

I had this same issue and it turns out it was because of how I was building the bundle.

If you're using webpack or browserify you need to "envify" it. There are places in the code base that look like this:

if (process.env.NODE_ENV !== "production") {
  doSomethingNotIE8Compatible()
}

To remove these, the react build uses the envify browserify transform to go and replace the process.env.NODE_ENV instances with the string with the value of your local terminal environmental variable.

For example, the first line becomes:

if ("production" !== "production") 

After this you should use uglify to remove the dead code to save size.

Finally, you need to run the code through an ES3-ifer to get rid of some small things that are legal in ES5 but not ES3. For example, catch function calls.

TLDR: at my company we have had a lot more success just using the CDN build rather than trying to get it bundling correctly.