internal/baseCallback.js

define(['./baseMatches', './baseProperty', './baseToString', './bindCallback', '../utility/identity', './isBindable'], function(baseMatches, baseProperty, baseToString, bindCallback, identity, isBindable) {

  /**
   * The base implementation of `_.callback` which supports specifying the
   * number of arguments to provide to `func`.
   *
   * @private
   * @param {*} [func=_.identity] The value to convert to a callback.
   * @param {*} [thisArg] The `this` binding of `func`.
   * @param {number} [argCount] The number of arguments to provide to `func`.
   * @returns {Function} Returns the callback.
   */
  function baseCallback(func, thisArg, argCount) {
    var type = typeof func;
    if (type == 'function') {
      return (typeof thisArg != 'undefined' && isBindable(func))
        ? bindCallback(func, thisArg, argCount)
        : func;
    }
    if (func == null) {
      return identity;
    }
    // Handle "_.property" and "_.matches" style callback shorthands.
    return type == 'object'
      ? baseMatches(func, !argCount)
      : baseProperty(argCount ? baseToString(func) : func);
  }

  return baseCallback;
});