Object.keys shim (non-spec-compliant): JavaScript vs CoffeeScript

objectkeys.txt

// JavaScript
if (Object.keys == null) {
    Object.keys = function(obj) {
        var keys = [];
        for (var key in obj) {
            if (obj.hasOwnProperty(key)) {
                keys.push(key);
            }
        }
        return keys;
    }
}

# CoffeeScript
Object.keys ?= (obj) ->
    key for key of obj when obj.hasOwnProperty(key)