1  var Stack = require('./_Stack'),
 2      assignMergeValue = require('./_assignMergeValue'),
 3      baseFor = require('./_baseFor'),
 4      baseMergeDeep = require('./_baseMergeDeep'),
 5      isObject = require('./isObject'),
 6      keysIn = require('./keysIn'),
 7      safeGet = require('./_safeGet');
 8  
 9  /**
10   * The base implementation of `_.merge` without support for multiple sources.
11   *
12   * @private
13   * @param {Object} object The destination object.
14   * @param {Object} source The source object.
15   * @param {number} srcIndex The index of `source`.
16   * @param {Function} [customizer] The function to customize merged values.
17   * @param {Object} [stack] Tracks traversed source values and their merged
18   *  counterparts.
19   */
20  function baseMerge(object, source, srcIndex, customizer, stack) {
21    if (object === source) {
22      return;
23    }
24    baseFor(source, function(srcValue, key) {
25      stack || (stack = new Stack);
26      if (isObject(srcValue)) {
27        baseMergeDeep(object, source, key, srcIndex, baseMerge, customizer, stack);
28      }
29      else {
30        var newValue = customizer
31          ? customizer(safeGet(object, key), srcValue, (key + ''), object, source, stack)
32          : undefined;
33  
34        if (newValue === undefined) {
35          newValue = srcValue;
36        }
37        assignMergeValue(object, key, newValue);
38      }
39    }, keysIn);
40  }
41  
42  module.exports = baseMerge;