[Typescript] 3 un-typed exports from @material-ui/core

[JonKrone]

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

@material-ui/core exports 3 references that are not available in the typescript definitions:

isString, isNumber, and styleFunction

Expected Behavior 🤔

@material-ui/core should either not export these variables or provide Typescript types for them.

Steps to Reproduce 🕹

See the testExports.ts file and the console output in this demo: https://codesandbox.io/s/optimistic-wilbur-98lq2

Context 🔦

We are trying to dynamically generate an index.ts file that re-exports all members of @material-ui/core, except those which we have defined in our wrapping library. e.g., we want to customize the function of the TextField elements, so want to override that element with our own export but just re-export most other Material components.

While generating this file, we realized that not all of the actually-exported members of @material-ui/core had types for them.

Your Environment 🌎

Tech	Version
Material-UI	v4.8.3

[oliviertassinari]

I don't think that any of the modules of styles/transitions.js, aside duration and easing, should be available in the barrel index. I would suggest:

diff --git a/packages/material-ui/src/styles/transitions.js b/packages/material-ui/src/styles/transitions.js
index 1cc6e1ad1..b4839a8a8 100644
--- a/packages/material-ui/src/styles/transitions.js
+++ b/packages/material-ui/src/styles/transitions.js
@@ -28,9 +28,9 @@ export const duration = {
   leavingScreen: 195,
 };

-export const formatMs = milliseconds => `${Math.round(milliseconds)}ms`;
-export const isString = value => typeof value === 'string';
-export const isNumber = value => !isNaN(parseFloat(value));
+function formatMs(milliseconds) {
+  return `${Math.round(milliseconds)}ms`;
+}

 /**
  * @param {string|Array} props
@@ -52,6 +52,9 @@ export default {
     } = options;

     if (process.env.NODE_ENV !== 'production') {
+      const isString = value => typeof value === 'string';
+      const isNumber = value => !isNaN(parseFloat(value));
+
       if (!isString(props) && !Array.isArray(props)) {
         console.error('Material-UI: argument "props" must be a string or Array.');
       }

I believe these methods were only exported recently with #18306.

[oliviertassinari]

Regarding styleFunction, the intent was to export and documented it for usage with styled-components and emotion, but it seems I never completed this task. Maybe we can remove the export now, and defer the concern to, later on, I'm wondering?

[JonKrone]

Awesome, I appreciate the speedy response.

If that is the approach you'd like to take for styleFunction, I would be happy to make these changes (probably later tonight/tomorrow), or if you want to take the time to document it now, I'll leave it for you as it'd take some time for me to do that properly.

[oliviertassinari]

For styleFunction, I don't know. I wish we can get more inputs on this matter.

[oliviertassinari]

@JonKrone Do you want to take care of the modules in styles/transitions.js :)?
(We can handle styleFunction later on)

[JonKrone]

Sure thing - made the above PR :).

There's probably a way to add this to the test suite. Could probably use the underlying typescript parser, ask it to generate a list of the symbols exported by the src/index.d.ts declaration file, then compare that with the list of symbols exported by a full module import/require.

(Just as an aside, I've +1'd the Issue thread about transitioning @material-ui to Typescript)