vitaliyserebryanskiy

const sum = data =>
  (data instanceof Array ? data : [ data ]).reduce((acc, n) => {
    return acc + n.value + sum(n.children || []);
  }, 0);

const sum = function(data) {
  const stack = [];
  let result = 0;

  for (let [ i, arr ] = this(data); ++i < arr.length || stack.length;) {
    if (i === arr.length) {
      [ i, arr ] = stack.pop();
    } else {
      result += arr[i].value;
      stack.push([ i, arr ]);
      [ i, arr ] = this(arr[i].children || []);
    }
  }

  return result;
}.bind(x => [ -1, Array.isArray(x) ? x : [ x ] ]);

sum(valueList) // 418
sum(valueList.children) // 268