index.js

function isErrorInstance(obj) {
  // eslint-disable-next-line prefer-reflect
  return obj instanceof Error || Object.prototype.toString.call(obj) === '[object Error]';
}

function isRegExp(obj) {
  // eslint-disable-next-line prefer-reflect
  return Object.prototype.toString.call(obj) === '[object RegExp]';
}

/**
 * ### .compatibleInstance(thrown, errorLike)
 *
 * Checks if two instances are compatible (strict equal).
 * Returns false if errorLike is not an instance of Error, because instances
 * can only be compatible if they're both error instances.
 *
 * @name compatibleInstance
 * @param {Error} thrown error
 * @param {Error|ErrorConstructor} errorLike object to compare against
 * @namespace Utils
 * @api public
 */

function compatibleInstance(thrown, errorLike) {
  return isErrorInstance(errorLike) && thrown === errorLike;
}

/**
 * ### .compatibleConstructor(thrown, errorLike)
 *
 * Checks if two constructors are compatible.
 * This function can receive either an error constructor or
 * an error instance as the `errorLike` argument.
 * Constructors are compatible if they're the same or if one is
 * an instance of another.
 *
 * @name compatibleConstructor
 * @param {Error} thrown error
 * @param {Error|ErrorConstructor} errorLike object to compare against
 * @namespace Utils
 * @api public
 */

function compatibleConstructor(thrown, errorLike) {
  if (isErrorInstance(errorLike)) {
    // If `errorLike` is an instance of any error we compare their constructors
    return thrown.constructor === errorLike.constructor || thrown instanceof errorLike.constructor;
  } else if ((typeof errorLike === 'object' || typeof errorLike === 'function') && errorLike.prototype) {
    // If `errorLike` is a constructor that inherits from Error, we compare `thrown` to `errorLike` directly
    return thrown.constructor === errorLike || thrown instanceof errorLike;
  }

  return false;
}

/**
 * ### .compatibleMessage(thrown, errMatcher)
 *
 * Checks if an error's message is compatible with a matcher (String or RegExp).
 * If the message contains the String or passes the RegExp test,
 * it is considered compatible.
 *
 * @name compatibleMessage
 * @param {Error} thrown error
 * @param {String|RegExp} errMatcher to look for into the message
 * @namespace Utils
 * @api public
 */

function compatibleMessage(thrown, errMatcher) {
  const comparisonString = typeof thrown === 'string' ? thrown : thrown.message;
  if (isRegExp(errMatcher)) {
    return errMatcher.test(comparisonString);
  } else if (typeof errMatcher === 'string') {
    return comparisonString.indexOf(errMatcher) !== -1; // eslint-disable-line no-magic-numbers
  }

  return false;
}

/**
 * ### .getConstructorName(errorLike)
 *
 * Gets the constructor name for an Error instance or constructor itself.
 *
 * @name getConstructorName
 * @param {Error|ErrorConstructor} errorLike
 * @namespace Utils
 * @api public
 */

function getConstructorName(errorLike) {
  let constructorName = errorLike;
  if (isErrorInstance(errorLike)) {
    constructorName = errorLike.constructor.name;
  } else if (typeof errorLike === 'function') {
    // If `err` is not an instance of Error it is an error constructor itself or another function.
    // If we've got a common function we get its name, otherwise we may need to create a new instance
    // of the error just in case it's a poorly-constructed error. Please see chaijs/chai/issues/45 to know more.
    constructorName = errorLike.name;
    if (constructorName === '') {
      const newConstructorName = (new errorLike().name); // eslint-disable-line new-cap
      constructorName = newConstructorName || constructorName;
    }
  }

  return constructorName;
}

/**
 * ### .getMessage(errorLike)
 *
 * Gets the error message from an error.
 * If `err` is a String itself, we return it.
 * If the error has no message, we return an empty string.
 *
 * @name getMessage
 * @param {Error|String} errorLike
 * @namespace Utils
 * @api public
 */

function getMessage(errorLike) {
  let msg = '';
  if (errorLike && errorLike.message) {
    msg = errorLike.message;
  } else if (typeof errorLike === 'string') {
    msg = errorLike;
  }

  return msg;
}

export { compatibleInstance, compatibleConstructor, compatibleMessage, getMessage, getConstructorName };