lodash/internal/createAssigner.js

import bindCallback from './bindCallback';
import isIterateeCall from './isIterateeCall';

/**
 * Creates a function that assigns properties of source object(s) to a given
 * destination object.
 *
 * @private
 * @param {Function} assigner The function to assign values.
 * @returns {Function} Returns the new assigner function.
 */
function createAssigner(assigner) {
  return function() {
    var length = arguments.length,
        object = arguments[0];

    if (length < 2 || object == null) {
      return object;
    }
    if (length > 3 && isIterateeCall(arguments[1], arguments[2], arguments[3])) {
      length = 2;
    }
    // Juggle arguments.
    if (length > 3 && typeof arguments[length - 2] == 'function') {
      var customizer = bindCallback(arguments[--length - 1], arguments[length--], 5);
    } else if (length > 2 && typeof arguments[length - 1] == 'function') {
      customizer = arguments[--length];
    }
    var index = 0;
    while (++index < length) {
      var source = arguments[index];
      if (source) {
        assigner(object, source, customizer);
      }
    }
    return object;
  };
}

export default createAssigner;