push() won't work as expected in reduce()

Question

Why doesn\'t a.push(b) work in my Array.reduce()? a=a.push(b) where b is a string, turns a to an integer.?!

Answer 1

The push() returns the new length. You can use ES2015 spread syntax:

var winner = objKeys.reduce((a, b)=> {
    a = (frequency[b] === highestVal)? [...a, b] : a;
    return a
}, []);