const sumArray = (numberArray) => { if (numberArray.length === 0) { return 0; } let addNumber = numberArray.shift(); if (typeof addNumber === 'object') { return sumArray(addNumber) + sumArray(numberArray); } else { return addNumber + sumArray(numberArray); } } console.log(sumArray([1,2,3,9])); console.log(sumArray([1, [2, 3, 4]])); console.log(sumArray([[2, 3, 4], [1, 1], 1]));