function/before.js

define(['../lang/isFunction'], function(isFunction) {

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

  /**
   * Creates a function that invokes `func`, with the `this` binding and arguments
   * of the created function, while it is called less than `n` times. Subsequent
   * calls to the created function return the result of the last `func` invocation.
   *
   * @static
   * @memberOf _
   * @category Function
   * @param {number} n The number of calls at which `func` is no longer invoked.
   * @param {Function} func The function to restrict.
   * @returns {Function} Returns the new restricted function.
   * @example
   *
   * jQuery('#add').on('click', _.before(5, addContactToList));
   * // => allows adding up to 4 contacts to the list
   */
  function before(n, func) {
    var result;
    if (!isFunction(func)) {
      if (isFunction(n)) {
        var temp = n;
        n = func;
        func = temp;
      } else {
        throw new TypeError(FUNC_ERROR_TEXT);
      }
    }
    return function() {
      if (--n > 0) {
        result = func.apply(this, arguments);
      } else {
        func = null;
      }
      return result;
    };
  }

  return before;
});