which object key has highest value javascript

1var obj = {a: 1, b: 2, undefined: 1};
2
3Object.keys(obj).reduce((a, b) => obj[a] > obj[b] ? a : b);

1var obj = {a: 1, b: 2, undefined: 1};
2
3Object.keys(obj).reduce((a, b) => obj[a] > obj[b] ? a : b);
4

1var obj = {a: 1, b: 2, undefined: 1};
2
3Object.keys(obj).reduce(function(a, b){ return obj[a] > obj[b] ? a : b });
4