Object.prototype.toString.call([]) returns incorrect result

[Rhionin]

The MDN-recommended way to check isArray is:

// Without Core-js
Object.prototype.toString.call([]) === '[object Array]'; // true

Core-js is replacing the array tag to be "Array Iterator" instead of "Array", which is breaking default behaviors which depend on it.

// With Core-js
Object.prototype.toString.call([]) === '[object Array]'; // false
Object.prototype.toString.call([]) === '[object Array Iterator]'; // true

In my case, core-js and CKEditor don't get along because CKEditor isn't even trying to use Array.isArray before using their own polyfill (see here). Note that I'm reporting to CKEditor that they should attempt to use Array.isArray before their polyfill, as that would make these compatible, but I still believe this is a concern as core-js is clobbering a default behavior.

[Rhionin]

Closing this. Turns out it was a combination of core-js and an older version of prototype.js (1.7.0), which is fixed when updating to 1.7.3. Y'all are great!