lodash/rest.js

define(['./internal/apply', './toInteger'], function(apply, toInteger) {

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

  /** Used as the `TypeError` message for "Functions" methods. */
  var FUNC_ERROR_TEXT = 'Expected a function';

  /* Built-in method references for those with the same name as other `lodash` methods. */
  var nativeMax = Math.max;

  /**
   * Creates a function that invokes `func` with the `this` binding of the
   * created function and arguments from `start` and beyond provided as an array.
   *
   * **Note:** This method is based on the [rest parameter](https://mdn.io/rest_parameters).
   *
   * @static
   * @memberOf _
   * @category Function
   * @param {Function} func The function to apply a rest parameter to.
   * @param {number} [start=func.length-1] The start position of the rest parameter.
   * @returns {Function} Returns the new function.
   * @example
   *
   * var say = _.rest(function(what, names) {
   *   return what + ' ' + _.initial(names).join(', ') +
   *     (_.size(names) > 1 ? ', & ' : '') + _.last(names);
   * });
   *
   * say('hello', 'fred', 'barney', 'pebbles');
   * // => 'hello fred, barney, & pebbles'
   */
  function rest(func, start) {
    if (typeof func != 'function') {
      throw new TypeError(FUNC_ERROR_TEXT);
    }
    start = nativeMax(start === undefined ? (func.length - 1) : toInteger(start), 0);
    return function() {
      var args = arguments,
          index = -1,
          length = nativeMax(args.length - start, 0),
          array = Array(length);

      while (++index < length) {
        array[index] = args[start + index];
      }
      switch (start) {
        case 0: return func.call(this, array);
        case 1: return func.call(this, args[0], array);
        case 2: return func.call(this, args[0], args[1], array);
      }
      var otherArgs = Array(start + 1);
      index = -1;
      while (++index < start) {
        otherArgs[index] = args[index];
      }
      otherArgs[start] = array;
      return apply(func, this, otherArgs);
    };
  }

  return rest;
});