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

javascript arrays reduce

Since push() returns the new length of the array, you're assigning the length to a. Instead of a conditional operator, use an if statement.

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

javascript arrays reduce

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}, []);

javascript arrays reduce

Building on the excellent answer by @Alexander Moiseyev.

You can avoid setting and mutating both variables a and winner by doing the following:

return objKeys.reduce((acc, val) =>    frequency[val] === highestVal       ? [...acc, val]       : acc,[])

note: for clarity I have explicitly declared the accumulator and value in this reduce method.

CodeHunter