Building tree using parent and child flat JSON structure

tree.js

var flatJSON = [
    {
      name : "A",
      parent : "root"
    },
    {
      name : "B",
      parent : "root"
    },
    {
      name : "C",
      parent: "A"
    },
    {
      name : "D",
      parent: "B"
    },
    {
      name : "E",
      parent: "C"
    },
    {
      name : "F",
      parent: "C"
    }
  ]

/** Class representing a Node in a tree. */
class Node {
    constructor(nodeName, parentName) {

        /** String of Node Name */
        this.name = nodeName;

        /** String of Parent Name */
        this.parentName = parentName;

        /** Array of Children. */
        this.children = [];
    }

}

function buildTree() {
  var tree = [],
      mappedArr = {},
      arrElem,
      mappedElem;

  // First map the nodes of the array to an object -> create a hash table.
  for (var i = 0, len = flatJSON.length; i < len; i++) {
    arrElem = new Node(flatJSON[i].name, flatJSON[i].parent);
    mappedArr[arrElem.name] = arrElem;
  }

  for (var name in mappedArr) {
    if (mappedArr.hasOwnProperty(name)) {
      mappedElem = mappedArr[name];
      // If the element is not at the root level, add it to its parentName array of children.
      if (mappedElem.parentName !== "root") {
        mappedArr[mappedElem['parentName']]['children'].push(mappedElem);
      } else { // If the element is at the root level, add it to first level elements array.
        tree.push(mappedElem);
      }
    }
  }
  console.log(tree);
}

buildTree();