index.js

'use strict';

/*
 * Module dependencies.
 */

var drop = require('@ndhoule/drop');
var rest = require('@ndhoule/rest');

var has = Object.prototype.hasOwnProperty;
var objToString = Object.prototype.toString;

/**
 * Returns `true` if a value is an object, otherwise `false`.
 *
 * @name isObject
 * @api private
 * @param {*} val The value to test.
 * @return {boolean}
 */
// TODO: Move to a library
var isObject = function isObject(value) {
  return Boolean(value) && typeof value === 'object';
};

/**
 * Returns `true` if a value is a plain object, otherwise `false`.
 *
 * @name isPlainObject
 * @api private
 * @param {*} val The value to test.
 * @return {boolean}
 */
// TODO: Move to a library
var isPlainObject = function isPlainObject(value) {
  return Boolean(value) && objToString.call(value) === '[object Object]';
};

/**
 * Assigns a key-value pair to a target object when the value assigned is owned,
 * and where target[key] is undefined.
 *
 * @name shallowCombiner
 * @api private
 * @param {Object} target
 * @param {Object} source
 * @param {*} value
 * @param {string} key
 */
var shallowCombiner = function shallowCombiner(target, source, value, key) {
  if (has.call(source, key) && target[key] === undefined) {
    target[key] = value;
  }
  return source;
};

/**
 * Assigns a key-value pair to a target object when the value assigned is owned,
 * and where target[key] is undefined; also merges objects recursively.
 *
 * @name deepCombiner
 * @api private
 * @param {Object} target
 * @param {Object} source
 * @param {*} value
 * @param {string} key
 * @return {Object}
 */
var deepCombiner = function(target, source, value, key) {
  if (has.call(source, key)) {
    if (isPlainObject(target[key]) && isPlainObject(value)) {
        target[key] = defaultsDeep(target[key], value);
    } else if (target[key] === undefined) {
        target[key] = value;
    }
  }

  return source;
};

/**
 * TODO: Document
 *
 * @name defaultsWith
 * @api private
 * @param {Function} combiner
 * @param {Object} target
 * @param {...Object} sources
 * @return {Object} Return the input `target`.
 */
var defaultsWith = function(combiner, target /*, ...sources */) {
  if (!isObject(target)) {
    return target;
  }

  combiner = combiner || shallowCombiner;
  var sources = drop(2, arguments);

  for (var i = 0; i < sources.length; i += 1) {
    for (var key in sources[i]) {
      combiner(target, sources[i], sources[i][key], key);
    }
  }

  return target;
};

/**
 * Copies owned, enumerable properties from a source object(s) to a target
 * object when the value of that property on the source object is `undefined`.
 * Recurses on objects.
 *
 * @name defaultsDeep
 * @api public
 * @param {Object} target
 * @param {...Object} sources
 * @return {Object} The input `target`.
 */
var defaultsDeep = function defaultsDeep(target /*, sources */) {
  // TODO: Replace with `partial` call?
  return defaultsWith.apply(null, [deepCombiner, target].concat(rest(arguments)));
};

/**
 * Copies owned, enumerable properties from a source object(s) to a target
 * object when the value of that property on the source object is `undefined`.
 *
 * @name defaults
 * @api public
 * @param {Object} target
 * @param {...Object} sources
 * @return {Object}
 * @example
 * var a = { a: 1 };
 * var b = { a: 2, b: 2 };
 *
 * defaults(a, b);
 * console.log(a); //=> { a: 1, b: 2 }
 */
var defaults = function(target /*, ...sources */) {
  // TODO: Replace with `partial` call?
  return defaultsWith.apply(null, [null, target].concat(rest(arguments)));
};

/*
 * Exports.
 */

module.exports = defaults;
module.exports.deep = defaultsDeep;