The spec explicitly says that we use the string form of the key (https://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.from).  I assume they've done that because the difference is noticible in some circumstance.  You can do `Array.from.call(MyArrayLikeClass, ...)` for instance.  Maybe you can see the difference between an integer and a string key using a proxy or something?  I don't know of any specific case where you'd be able to tell the difference in es5 engines, so I'm fine with leaving off the `String` conversion if you prefer.  I just added it because it was in the spec...