perf: isPlainObject: add quick comparison between input and Object to short-circuit taxing Function.toString invocations

[benelliott]

Fixes #804

[mweststrate]

Thanks for optimising this!

[mweststrate]

🎉 This PR is included in version 9.0.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[markerikson]

FWIW, here's the implementation that Redux uses:

https://github.com/reduxjs/redux/blob/master/src/utils/isPlainObject.ts

/**
 * @param obj The object to inspect.
 * @returns True if the argument appears to be a plain object.
 */
export default function isPlainObject(obj: any): boolean {
  if (typeof obj !== 'object' || obj === null) return false

  let proto = obj
  while (Object.getPrototypeOf(proto) !== null) {
    proto = Object.getPrototypeOf(proto)
  }

  return Object.getPrototypeOf(obj) === proto
}

I believe this also correctly handles cross-frame behavior. If I remember right, @timdorr implemented this. Backstory:

• Using lodash.isPlainObject in dispatch has performance overhead reduxjs/redux#2598
• Optimize dispatch plain object check reduxjs/redux#2599