Code example that introduces TypeError.

[LAITONEN]

• This is a v1.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

The problem is here:

1. Link: https://material-ui.com/demos/menus/#simple-menu
2. Open the Source Code of the first example in Simple Menu section.

I have a TypeScript project, where I decided to use Menu Component. After copy-pasting the code from the documentation, I got this TypeError for Menu Component:

Type 'null' is not assignable to type 'HTMLElement | undefined'.

Which means that the value of anchorEl can not be null, whereas the documentation implies that it could. Setting the value of anchorEl to undefined solves the problem.

Your Environment

Tech	Version
Material-UI	v1.0.0-beta.26
Typescript	2.8.3
VS Code	1.25.1

[oliviertassinari]

@LAITONEN We have been fixing the very same issue a few days ago for the Popper component. We need to change this line
https://github.com/mui-org/material-ui/blob/ba2ba252c2389cdde4e44d0ccb149c6ba466b349/packages/material-ui/src/Menu/Menu.d.ts#L11
as it was done here: #12161 (comment)
Do you want to work on it?

[LAITONEN]

@oliviertassinari I could. You think it is the typing that should be corrected, not the default value of this.state.anchorEl in the example (from null to undefined)?

[oliviertassinari]

@LAITONEN I'm suggesting that we change material-ui/packages/material-ui/src/Menu/Menu.d.ts as we did for the Popper: #12161 (comment):

-  anchorEl?: HTMLElement | ((element: HTMLElement) => HTMLElement);
+  anchorEl?: null | HTMLElement | ((element: HTMLElement) => HTMLElement);