lodash/internal/baseMergeDeep.js

define(['./assignMergeValue', './baseClone', './copyArray', '../isArguments', '../isArray', '../isArrayLikeObject', '../isFunction', '../isObject', '../isPlainObject', '../isTypedArray', '../toPlainObject'], function(assignMergeValue, baseClone, copyArray, isArguments, isArray, isArrayLikeObject, isFunction, isObject, isPlainObject, isTypedArray, toPlainObject) {

  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
  var undefined;

  /**
   * A specialized version of `baseMerge` for arrays and objects which performs
   * deep merges and tracks traversed objects enabling objects with circular
   * references to be merged.
   *
   * @private
   * @param {Object} object The destination object.
   * @param {Object} source The source object.
   * @param {string} key The key of the value to merge.
   * @param {Function} mergeFunc The function to merge values.
   * @param {Function} [customizer] The function to customize assigned values.
   * @param {Object} [stack] Tracks traversed source values and their merged counterparts.
   */
  function baseMergeDeep(object, source, key, mergeFunc, customizer, stack) {
    var objValue = object[key],
        srcValue = source[key],
        stacked = stack.get(srcValue) || stack.get(objValue);

    if (stacked) {
      assignMergeValue(object, key, stacked);
      return;
    }
    var newValue = customizer ? customizer(objValue, srcValue, (key + ''), object, source, stack) : undefined,
        isCommon = newValue === undefined;

    if (isCommon) {
      newValue = srcValue;
      if (isArray(srcValue) || isTypedArray(srcValue)) {
        newValue = isArray(objValue)
          ? objValue
          : ((isArrayLikeObject(objValue)) ? copyArray(objValue) : baseClone(srcValue));
      }
      else if (isPlainObject(srcValue) || isArguments(srcValue)) {
        newValue = isArguments(objValue)
          ? toPlainObject(objValue)
          : (isObject(objValue) ? objValue : baseClone(srcValue));
      }
      else {
        isCommon = isFunction(srcValue);
      }
    }
    stack.set(srcValue, newValue);

    if (isCommon) {
      // Recursively merge objects and arrays (susceptible to call stack limits).
      mergeFunc(newValue, srcValue, customizer, stack);
    }
    assignMergeValue(object, key, newValue);
  }

  return baseMergeDeep;
});