Rule proposal: `isArray()` rather than `instanceof Array`

I’d like to propose a new rule: that checking for <foo> instanceof Array and suggesting that it should be rewritten as Array.isArray(<foo>).

Using instanceof Array can return false when checking an array object created by another window (or possibly another process on node?), whereas Array.isArray() would work as expected. A more in-depth discussion can be found here.

What category of rule is this? (place an “X” next to just one item)

[ ] Enforces code style [x] Warns about a potential error [ ] Suggests an alternate way of doing something [ ] Other (please specify:)

Provide 2-3 code examples that this rule will warn about:

if (anArray instanceof Array) {
    // do something...
}

var foo = anArray instanceof Array ? true : false

Why should this rule be included in ESLint (instead of a plugin)?

My assumption is that this issue is core to both javascript in the browser and node.js, so I would assume it should go into ESLint itself. Array.isArray() has been supported in JavaScript since ES5.

[mysticatea]

FWIW, I have the rule in my plugin: https://github.com/mysticatea/eslint-plugin#book-usage

[platinumazure]

@ljharb You’re certainly welcome to lay out a proposal. To be honest, I don’t know how I feel about that at this point.