binary-tree-max-sum.js

var node = {
  value: -120,
  left: {
    value: -2120,
    left: { value: -20 },
    right: { value: -30 }
  },
  right: {
    value: -20,
    left: {value: 20 },
    right: { value: 300 }
  }
};

function getMax(x) {
  if (typeof x === 'undefined' || x === null) {
    return 0;
  }
  var left = getMax(x.left);
  var right = getMax(x.right);
  return x.value + Math.max(left, right);
}
console.log(getMax(node));