Argument checking simplification

gistfile1.js

if (!String.prototype.capitalize) {
  String.prototype.capitalize = function() {
    return this.charAt(0).toUpperCase() + this.slice(1);
  }
}


function assertArg(name, type) {
  if (typeof(name) !== type)
    throw new TypeError(name + '(' + type.capitalize() + ') required');
}


CA.prototype.listSchema = function(customer, callback) {
  assertArg(customer, 'string');
  assertArg(callback, 'function');

  var path = sprintf(CA_FMT, customer);
  return this.client.get(path, commonCallback(callback));
};