react-is: 16.12.0 isMemo is returning wrong value

[changran52m]

Bug in react-is: 16.12.0
https://codesandbox.io/s/determined-lehmann-hl43r

This issue does not exist in ### 16.11.0
https://codesandbox.io/s/nifty-paper-8cqil

[milesj]

This changed in v16.12: #17278

[changran52m]

This changed in v16.12: #17278

@milesj Thanks for your quick reply.
However, I am still able to reproduce it here. Please correct me if I am wrong.

https://codesandbox.io/s/determined-lehmann-hl43r

import React, { memo } from "react";

import { isMemo } from "react-is";

const Test = memo(() => {
  return <div>test</div>;
});

console.log("Test", isMemo(Test)); // false

[changran52m]

@milesj
I think I get it now. It was a bug and got fixed in 16.12. But seems there are so many packages depending on the buggy function.

I will try some work around in our side and open issue in material UI and enzyme repo then.

Thanks again for your quick reply.

[bvaughn]

As the linked PR #17278 mentions:

const MemoizedComponent = React.memo(MyComponent);

// MemoizedComponent is a valid element TYPE.
expect(ReactIs.isValidElementType(MemoizedComponent)).toBe(true);

// <MemoizedComponent /> is a valid element.
expect(ReactIs.typeOf(<MemoizedComponent />)).toBe(ReactIs.Memo);
expect(ReactIs.isMemo(<MemoizedComponent />)).toBe(true);

// MemoizedComponent is NOT an element!
// (This used to return a false positive.)
expect(ReactIs.isMemo(MemoizedComponent)).toBe(false);

The previous behavior was broken. It's unfortunate that the bug fix caused some existing use cases to "break" but I think it was still the right change to make.

Sorry for the inconvenience!