lodash/_createAssigner.js

define(['./_baseRest', './_isIterateeCall'], function(baseRest, isIterateeCall) {

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

  /**
   * Creates a function like `_.assign`.
   *
   * @private
   * @param {Function} assigner The function to assign values.
   * @returns {Function} Returns the new assigner function.
   */
  function createAssigner(assigner) {
    return baseRest(function(object, sources) {
      var index = -1,
          length = sources.length,
          customizer = length > 1 ? sources[length - 1] : undefined,
          guard = length > 2 ? sources[2] : undefined;

      customizer = (assigner.length > 3 && typeof customizer == 'function')
        ? (length--, customizer)
        : undefined;

      if (guard && isIterateeCall(sources[0], sources[1], guard)) {
        customizer = length < 3 ? undefined : customizer;
        length = 1;
      }
      object = Object(object);
      while (++index < length) {
        var source = sources[index];
        if (source) {
          assigner(object, source, index, customizer);
        }
      }
      return object;
    });
  }

  return createAssigner;
});