positiveSum one line version
tweaked solution with examples for shortest code
by trentHarlem
JavaScript
const positiveSum = (arr) => arr.filter(x => x >= 0).reduce((a, b) => a + b, 0)
console.log(positiveSum([1, 2, 3, 4, 5]), '15')
console.log(positiveSum([1, -2, 3, 4, 5]), '13') //.filter catches -2
console.log(positiveSum([]), '0') // initial value in .reduce
console.log(positiveSum([-1, -2, -3, -4, -5]), '0') // initial value in .reduce