Possible Preact 8 regression: Cannot read property 'toLowerCase' of undefined

Looks like it’s during VDOM diffing

Error occurs in isNamedNode https://github.com/developit/preact/blob/52bb91e17a56e6f3dba050c3ae001292b6ff2285/src/vdom/index.js#L27

Stack (bundled) is

Uncaught TypeError: Cannot read property 'toLowerCase' of undefined
    at isNamedNode (vendor-bfd2f8511748e755b3c2.js:2619)
    at idiff (vendor-bfd2f8511748e755b3c2.js:2399)
    at innerDiffNode (vendor-bfd2f8511748e755b3c2.js:2502)
    at idiff (vendor-bfd2f8511748e755b3c2.js:2426)
    at diff (vendor-bfd2f8511748e755b3c2.js:2347)
    at renderComponent (vendor-bfd2f8511748e755b3c2.js:1121)
    at renderComponent (vendor-bfd2f8511748e755b3c2.js:1106)
    at setComponentProps (vendor-bfd2f8511748e755b3c2.js:1028)
    at buildComponentFromVNode (vendor-bfd2f8511748e755b3c2.js:1203)
    at idiff (vendor-bfd2f8511748e755b3c2.js:2393)

Let me know if you need more info.

[developit]

Null renders are okay, they don’t throw. This only happens when you render a component with no constructor:

const Okay = () => null;   // all good

let Foo;  // undefined
const NotOkay = () => <Foo />;    // not good - h(Foo) = h(undefined)

[developit]

Awesome! Yeah sortof an odd bug here.

FWIW I think we’re going to revert the throw here. It’s nice to make people aware of undefined components, but it’s probably a little too harsh to break rendering when encountering them. That plugin is going to find it’s way into a wrapper around preact/devtools, where we’ll be adding a bunch of debugging tips & helpers:

if (process.env.NODE_ENV==='development') {
  // enables devtools & things like undefined component warnings:
  require('preact/debug');
}