config.js

export const config = {

  /**
   * ### config.includeStack
   *
   * User configurable property, influences whether stack trace
   * is included in Assertion error message. Default of false
   * suppresses stack trace in the error message.
   *
   *     chai.config.includeStack = true;  // enable stack on error
   *
   * @param {boolean}
   * @public
   */
  includeStack: false,

  /**
   * ### config.showDiff
   *
   * User configurable property, influences whether or not
   * the `showDiff` flag should be included in the thrown
   * AssertionErrors. `false` will always be `false`; `true`
   * will be true when the assertion has requested a diff
   * be shown.
   *
   * @param {boolean}
   * @public
   */
  showDiff: true,

  /**
   * ### config.truncateThreshold
   *
   * User configurable property, sets length threshold for actual and
   * expected values in assertion errors. If this threshold is exceeded, for
   * example for large data structures, the value is replaced with something
   * like `[ Array(3) ]` or `{ Object (prop1, prop2) }`.
   *
   * Set it to zero if you want to disable truncating altogether.
   *
   * This is especially userful when doing assertions on arrays: having this
   * set to a reasonable large value makes the failure messages readily
   * inspectable.
   *
   *     chai.config.truncateThreshold = 0;  // disable truncating
   *
   * @param {number}
   * @public
   */
  truncateThreshold: 40,

  /**
   * ### config.useProxy
   *
   * User configurable property, defines if chai will use a Proxy to throw
   * an error when a non-existent property is read, which protects users
   * from typos when using property-based assertions.
   *
   * Set it to false if you want to disable this feature.
   *
   *     chai.config.useProxy = false;  // disable use of Proxy
   *
   * This feature is automatically disabled regardless of this config value
   * in environments that don't support proxies.
   *
   * @param {boolean}
   * @public
   */
  useProxy: true,

  /**
   * ### config.proxyExcludedKeys
   *
   * User configurable property, defines which properties should be ignored
   * instead of throwing an error if they do not exist on the assertion.
   * This is only applied if the environment Chai is running in supports proxies and
   * if the `useProxy` configuration setting is enabled.
   * By default, `then` and `inspect` will not throw an error if they do not exist on the
   * assertion object because the `.inspect` property is read by `util.inspect` (for example, when
   * using `console.log` on the assertion object) and `.then` is necessary for promise type-checking.
   *
   *     // By default these keys will not throw an error if they do not exist on the assertion object
   *     chai.config.proxyExcludedKeys = ['then', 'inspect'];
   *
   * @param {Array}
   * @public
   */
  proxyExcludedKeys: ['then', 'catch', 'inspect', 'toJSON'],

  /**
   * ### config.deepEqual
   *
   * User configurable property, defines which a custom function to use for deepEqual
   * comparisons.
   * By default, the function used is the one from the `deep-eql` package without custom comparator.
   *
   *     // use a custom comparator
   *     chai.config.deepEqual = (expected, actual) => {
   *         return chai.util.eql(expected, actual, {
   *             comparator: (expected, actual) => {
   *                 // for non number comparison, use the default behavior
   *                 if(typeof expected !== 'number') return null;
   *                 // allow a difference of 10 between compared numbers
   *                 return typeof actual === 'number' && Math.abs(actual - expected) < 10
   *             }
   *         })
   *     };
   *
   * @param {Function}
   * @public
   */
  deepEqual: null

};