callback wrapper for node.js

cbwrap.js

/**
 * Wrap a node callback so that it doesn't have to do error-checking.
 * Returns a function that checks for an error as the first argument.
 * If the error is truthy and you provided an error handler, it passes
 * the error to this function. Otherwise it calls cb with the error.
 * If there was no error and you provided an error handler, it
 * only passes the remaining arguments to cb. Otherwise it passes
 * null as the first argument (the error).
 * 
 * @param  {Function}   cb - function(err, ...) or function(...)
 * @param  {Function}   [errorHandler] - Optional function(err)
 */
function cbwrap(cb, errorHandler) {
  if (!_.isFunction(cb)) {
    throw new TypeError('cbwrap expects a function argument');
  }
  return function(err) {
    if (err) {
      if (typeof errorHandler === 'function') {
        errorHandler(err);
      } else {
        cb(err);
      }
    } else {
      var args = Array.prototype.slice.call(arguments, 1);
      if (typeof errorHandler === 'function') {
        // if an error handler was provided, cb should not care
        // about the error
        cb.apply(cb, args);
      } else {
        cb.apply(cb, [null].concat(args));
      }
    }
  };
}