101/pick.js

common javascript utils that can be required selectively that assume es5+

/**
 * @module 101/pick
 */

var exists = require('./exists');
var isObject = require('./is-object');
var isRegExp = require('./is-regexp');
var isString = require('./is-string');
var keypather = require('keypather')();
var isKeypath = function (val) {
  return Array.isArray(val) || isString(val) || isRegExp(val)
}

/**
 * Returns a new object with the specified keys (with key values from obj).
 * When only keys are specified pick returns a partial-function which accepts obj.
 * @function module:101/pick
 * @param {object} [obj] - object whose keys are picked
 * @param {string|regexp|array} keys... - keys which will be taken from obj, can be specifieds as args (strings, regular epxressions, and/or arrays)
 * @return {object|function} Object with only the keys specified from the original obj or Partial-function pick (which accepts obj) and returns an object
 */
module.exports = function () {
  var args = Array.prototype.slice.call(arguments);
  if (exists(args[0]) && !isKeypath(args[0])) {
    var obj = args.shift();
    return pick(obj, args);
  } else {
    return function (obj) {
      return pick(obj, args);
    };
  }
};

function pick (obj, args) {
  var keys = [];
  args.forEach(function (key) {
    keys = keys.concat(key);
  });
  var out = {};
  keys.forEach(copy(obj, out));
  return out;
}

function copy (from, to) {
  return function (key) {
    if (isRegExp(key)) {
      var flatFrom = keypather.flatten(from);
      Object.keys(flatFrom).forEach(function(keypathFrom) {
        if (key.test(keypathFrom)) {
          keypather.set(to, keypathFrom, keypather.get(from, keypathFrom));
        }
      });
    } else {
      if (keypather.in(from, key)) {
        keypather.set(to, key, keypather.get(from, key));
      }
    }
  };
}