ninjajs-mfr1.js

const positiveSum = arr => {
  let sum = 0
  let i = 0
  let ii = arr.length
  for (i = 0; i < ii; ++i) {
    if (arr[i] > 0) {
      sum += arr[i]
    }
  }
}

// A more elegant approach
const positiveSum = arr => arr
  .filter(num => num > 0)
  .reduce((a, b) => a + b)

// Even shorter
const positiveSum = arr => arr
  .reduce((acc, v) => Math.max(acc, acc + v), 0)