I don't agree with GP's sentiment but one need only look at Number.parseInt vs parseInt and the associates coercion differences, and even typeof null which was on the front page today. Lots of cumbersome APIs like XHR and others designed before Promises existed, and even smooshgate, where we couldn't introduce flatten() because Prototype (iirc) implemented it already and failed to properly handle the possibility that the browser could already have it (plus it worked differently where the default depth of the new standard API is 2).