gremlins-ts/src/mogwais/gizmo.ts

A monkey testing library written in JavaScript, for Node.js and the browser. Use it to check the robustness of web applications by unleashing a horde of undisciplined gremlins.

import { configurable } from "../utils";
/**
 * Gizmo is a special mogwai who can stop the gremlins when they go too far
 *
 * The gizmo mogwai monitors the JavaScript alerts and the calls to
 * console.alert(), and stops the stress test execution once the number of
 * errors pass a certain threshold (10 errors by default).
 *
 *   var gizmoMogwai = gremlins.mogwais.gizmo();
 *   horde.mogwai(gizmoMogwai);
 *
 * The gizmo mogwai can be customized as follows:
 *
 *   gizmoMogwai.maxErrors(10); // the number of errors after which the test stops
 *   gizmoMogwai.logger(loggerObject); // inject a logger
 *
 * Example usage:
 *
 *   horde.mogwai(gremlins.mogwais.gizmo()
 *     .maxErrors(5)
 *   );
 */
type Config = {
  maxErrors: number;
  logger: typeof console;
};
export function gizmo() {
  const config: Config = {
    maxErrors: 10,
    logger: console
  };

  let realOnError: Window["onerror"];
  let realLoggerError: typeof console["error"];

  function gizmoMogwai() {
    let nbErrors = 0;
    // @ts-ignore
    let horde = this; // this is exceptional - don't use 'this' for mogwais in general
    function incrementNbErrors() {
      nbErrors++;
      if (nbErrors >= config.maxErrors) {
        horde.stop();
        if (!config.logger) return;
        window.setTimeout(function() {
          // display the mogwai error after the caught error
          config.logger.warn(
            "mogwai ",
            "gizmo     ",
            "stopped test execution after ",
            config.maxErrors,
            "errors"
          );
        }, 4);
      }
    }

    // general JavaScript errors
    realOnError = window.onerror;
    window.onerror = function(message, url, linenumber) {
      incrementNbErrors();
      return realOnError ? realOnError(message, url, linenumber) : false;
    };

    // console errors
    realLoggerError = console.error;
    console.error = (...args: string[]) => {
      incrementNbErrors();
      realLoggerError.call(console, ...args);
    };
  }

  gizmoMogwai.cleanUp = () => {
    window.onerror = realOnError;
    console.error = realLoggerError.bind(console);
    return gizmoMogwai;
  };

  configurable(gizmoMogwai, config);

  return gizmoMogwai;
}