Update is-shallow-equal to use ES5 code as before

[gziolo]

Description

Closes #8048.

Fixes an issue raised by @nerrad in #8048:

The docs for this package describe being able to import two specific exports for is-shallow-equal:

You can import a specific implementation if you already know the types of values you are working with:

import isShallowEqualArrays from '@wordpress/is-shallow-equal/arrays';
import isShallowEqualObjects from '@wordpress/is-shallow-equal/objects';

However, with the latest release of the package this no longer works. When building using webpack, the build fails with:

ERROR in ./src/index.js
Module not found: Error: Can't resolve '@wordpress/is-shallow-equal/arrays'

I followed recommendation from @aduth:

The root cause of this is that the require semantics were expecting arrays.js and objects.js files in the root module directory. These no longer exist (they live in build), as apparently the package is now subject to the transpile build step (it was not originally).

and reverted the change I introduce when merging this package into Gutenber repository in #7556.

How has this been tested?

• npm test passes
• both npm run dev and npm run build work as before

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[nerrad]

Looks good (aside from the linting issue with package.json). I copied the changes into the @wordpress/is-shallow-equal package in my dummy app importing it and there's no build errors now.

[nerrad]

package.json linting failed with this:

./packages/is-shallow-equal/package.json
[0] ✖ prefer-property-order - node:  - Your package.json properties are not in the desired order. Please move "main" after "files".

[gziolo]

Ha, correct. Our linter is very strict 😄

[aduth]

Note for future reference in extracting rules: We should consider having separate rulesets for ES5 vs. ES2015+ .

Looks like this is already built-in to eslint-plugin-wordpress:

https://github.com/WordPress-Coding-Standards/eslint-plugin-wordpress#available-rulesets

(Confused why there's both a config and a plugin which includes rulesets)

[gziolo]

Agreed, it would be much easier to put the following:

{
    "root": true,
    "extends": "something"
}

[aduth]

Yeah, I do this in my own projects, where (like with this one) I sometimes intentionally author in ES5.

https://github.com/aduth/memize/blob/4c0c9f9/.eslintrc.json#L3
https://github.com/aduth/equivalent-key-map/blob/e80140c/.eslintrc.json#L3