flattenTreeByChildren & makeTreeWithParentId

datatree.js

var util = {
          i: 0,
        	uuid: function() {return this.i++},
          copyObj: function(obj) {
              var result = Array.isArray(obj) ? [] : {};
              for (var key in obj) result[key] = obj[key];
              return result;
          }
        };

function flattenTreeByChildren(data, parentId) {
            var result = data.map(function(item) {
                var result = util.copyObj(item);
                result.children = null;
                result.parentId = parentId;
                return result;
            });
            for (var index in data) {
                if (
                    data[index] 
                    && data[index].children 
                    && data[index].children.length
                ) {
                    result = result.concat(flattenTreeByChildren(data[index].children, data[index].id))
                }
            }
            return result;
        }

        function makeTreeWithParentId(data) {
            var result = [];
            var getItemById = function (data, id) {
                for (var index in data) {
                    if (data[index] && data[index].id === id) {
                        return data[index]
                    }
                }
            };

            data.forEach(function(item) {
                if (!item.parentId) {
                    result.push(item);
                    return;
                }
                var parentItem = getItemById(data, item.parentId);
                parentItem.children = parentItem.children || [];
                parentItem.children.push(item);
            });

            return result;
        }