lodash-es/internal/baseMerge.js

The modern build of lodash exported as ES modules.

import arrayEach from './arrayEach';
import baseMergeDeep from './baseMergeDeep';
import isArray from '../lang/isArray';
import isArrayLike from './isArrayLike';
import isObject from '../lang/isObject';
import isObjectLike from './isObjectLike';
import isTypedArray from '../lang/isTypedArray';
import keys from '../object/keys';

/**
 * The base implementation of `_.merge` without support for argument juggling,
 * multiple sources, and `this` binding `customizer` functions.
 *
 * @private
 * @param {Object} object The destination object.
 * @param {Object} source The source object.
 * @param {Function} [customizer] The function to customize merged values.
 * @param {Array} [stackA=[]] Tracks traversed source objects.
 * @param {Array} [stackB=[]] Associates values with source counterparts.
 * @returns {Object} Returns `object`.
 */
function baseMerge(object, source, customizer, stackA, stackB) {
  if (!isObject(object)) {
    return object;
  }
  var isSrcArr = isArrayLike(source) && (isArray(source) || isTypedArray(source)),
      props = isSrcArr ? undefined : keys(source);

  arrayEach(props || source, function(srcValue, key) {
    if (props) {
      key = srcValue;
      srcValue = source[key];
    }
    if (isObjectLike(srcValue)) {
      stackA || (stackA = []);
      stackB || (stackB = []);
      baseMergeDeep(object, source, key, baseMerge, customizer, stackA, stackB);
    }
    else {
      var value = object[key],
          result = customizer ? customizer(value, srcValue, key, object, source) : undefined,
          isCommon = result === undefined;

      if (isCommon) {
        result = srcValue;
      }
      if ((result !== undefined || (isSrcArr && !(key in object))) &&
          (isCommon || (result === result ? (result !== value) : (value === value)))) {
        object[key] = result;
      }
    }
  });
  return object;
}

export default baseMerge;