Came across an error for hasOwnProperty when adding this.storeKeys to a React component listening to a Reflux store. So I:

• Stripped the component down to just a few lines; still errored
• Pointed to a different store; still errored
• Cleared cache and restarted the web server; still errored
• Looked at the store – bingo!

This error pops up when trying to listen to a store from an older version of Reflux. Updating the store to the new format will fix it, or you can bind to the store the old Reflux way.