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

Please note that this structure you provide is not clear enough

I would use instead an array of objects each having a name and a frecuency

var frequencies = [{name : "mats", frecuency : 1},
                   {name : "john", frecuency: 3},
                   {name : "johan", frecuency: 2},
                   {name : "jacob", frecuency: 3}];

Then you can use a filter operation and map to get what you need

var max = Math.max.apply(Math, frequencies.map(function(o){return o.frecuency;}));
var maxElems = frequencies.filter(function(a){return a.frecuency == max}).map(function(a){return a.name;});

maxElems will give you the names of the people with higher frecuency

Answer 2

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;
}, []);

Answer 3

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.

Answer 4

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
}, []);