index.js

'use strict';
var property = require('nested-property');
var keyBy = require('lodash.keyby');

function createTree(array, rootNodes, customID, childrenProperty) {
  var tree = [];

  for (var rootNode in rootNodes) {
    var node = rootNodes[rootNode];
    var childNode = array[node[customID]];

    if (!node && !rootNodes.hasOwnProperty(rootNode)) {
      continue;
    }

    if (childNode) {
      node[childrenProperty] = createTree(
        array,
        childNode,
        customID,
        childrenProperty
      );
    }

    tree.push(node);
  }

  return tree;
}

function groupByParents(array, options) {
  var arrayByID = keyBy(array, options.customID);

  return array.reduce(function(prev, item) {
    var parentID = property.get(item, options.parentProperty);
    if (!parentID || !arrayByID.hasOwnProperty(parentID)) {
      parentID = options.rootID;
    }

    if (parentID && prev.hasOwnProperty(parentID)) {
      prev[parentID].push(item);
      return prev;
    }

    prev[parentID] = [item];
    return prev;
  }, {});
}

function isObject(o) {
  return Object.prototype.toString.call(o) === '[object Object]';
}

function deepClone(data) {
  if (Array.isArray(data)) {
    return data.map(deepClone);
  } else if (isObject(data)) {
    return Object.keys(data).reduce(function(o, k) {
      o[k] = deepClone(data[k]);
      return o;
    }, {});
  } else {
    return data;
  }
}

/**
 * arrayToTree
 * Convert a plain array of nodes (with pointers to parent nodes) to a nested
 * data structure
 *
 * @name arrayToTree
 * @function
 *
 * @param {Array} data An array of data
 * @param {Object} options An object containing the following fields:
 *
 *  - `parentProperty` (String): A name of a property where a link to
 * a parent node could be found. Default: 'parent_id'
 *  - `customID` (String): An unique node identifier. Default: 'id'
 *  - `childrenProperty` (String): A name of a property where children nodes
 * are going to be stored. Default: 'children'.
 *
 * @return {Array} Result of transformation
 */

module.exports = function arrayToTree(data, options) {
  options = Object.assign(
    {
      parentProperty: 'parent_id',
      childrenProperty: 'children',
      customID: 'id',
      rootID: '0'
    },
    options
  );

  if (!Array.isArray(data)) {
    throw new TypeError('Expected an array but got an invalid argument');
  }

  var grouped = groupByParents(deepClone(data), options);
  return createTree(
    grouped,
    grouped[options.rootID],
    options.customID,
    options.childrenProperty
  );
};