negate.js

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

/**
 * Creates a function that negates the result of the predicate `func`. The
 * `func` predicate is invoked with the `this` binding and arguments of the
 * created function.
 *
 * @static
 * @memberOf _
 * @category Function
 * @param {Function} predicate The predicate to negate.
 * @returns {Function} Returns the new function.
 * @example
 *
 * function isEven(n) {
 *   return n % 2 == 0;
 * }
 *
 * _.filter([1, 2, 3, 4, 5, 6], _.negate(isEven));
 * // => [1, 3, 5]
 */
function negate(predicate) {
  if (typeof predicate != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  return function() {
    return !predicate.apply(this, arguments);
  };
}

module.exports = negate;