TypeError: mobx.defineProperty is not a function

[davetapley]

Putting this here for Google in case it catches others out

I bumped mobx-state-tree in my package.json and started getting:

TypeError: mobx.defineProperty is not a function

[davetapley]

Check npm install for:

npm WARN mobx-state-tree@5.1.5 requires a peer of mobx@^6.3.0 but none is installed. You must install peer dependencies yourself.

Then update your package.json to have:

"mobx": "^6.3.0",

Then npm install again and restart everything.