Description:
You get an array of numbers, return the sum of all of the positives ones.
Example [1,-4,7,12] => 1 + 7 + 12 = 20
Note: if there is nothing to sum, the sum is default to 0.
function positiveSum(arr) {
return arr.filter(el => el > 0).reduce((a,b) => a+b,0)
}