conveyal/modeify

var next = require('../../../timoxley/next-tick/0.0.2');


/**
 * Expose `callback`.
 */

module.exports = callback;


/**
 * Call an `fn` back synchronously if it exists.
 *
 * @param {Function} fn
 */

function callback (fn) {
  if ('function' === typeof fn) fn();
}


/**
 * Call an `fn` back asynchronously if it exists. If `wait` is ommitted, the
 * `fn` will be called on next tick.
 *
 * @param {Function} fn
 * @param {Number} wait (optional)
 */

callback.async = function (fn, wait) {
  if ('function' !== typeof fn) return;
  if (!wait) return next(fn);
  setTimeout(fn, wait);
};


/**
 * Symmetry.
 */

callback.sync = callback;