Uncaught TypeError: Cannot read property ‘toUpperCase’ of undefined in React
Ok, I gotta admit this is a really annoying issue because its root cause is pretty trivial.
You get this issue in React when
You are accidentally trying to render a component and that component itself is null or undefined. e.g you are trying to render
<MyComponent />when the value of
MyComponentis itself null or undefined.
Ive encountered this issue several times, the most recent being when upgrading to react-router 1.0 release candidate which eliminated the the
<RouteHandler /> component. As a result, at places in my tree where I was doing a require for
RouteHandler, things worked because it simply returned undefiend, but the moment I tried to render it using
<RouteHandler /> React gave me this pretty little error.
Hope this helps you save some productive time!