unction'))) {
    operator = 'strictEqualObject';
  }

  // If "actual" and "expected" fit on a single line and they are not strictly
  // equal, check further special handling.
  if (actualLines.length === 1 && expectedLines.length === 1 &&
    actualLines[0] !== expectedLines[0]) {
    // Check for the visible length using the `removeColors()` function, if
    // appropriate.
    const c = inspect.defaultOptions.colors;
    const actualRaw = c ? removeColors(actualLines[0]) : actualLines[0];
    const expectedRaw = c ? removeColors(expectedLines[0]) : expectedLines[0];
    const inputLength = actualRaw.length + expectedRaw.length;
    // If the character length of "actual" and "expected" together is less than
    // kMaxShortLength and if neither is an object and at least one of them is
    // not `zero`, use the strict equal comparison to visualize the output.
    if (inputLength <= kMaxShortLength) {
      if ((typeof actual !== 'object' || actual === null) &&
          (typeof expected !== 'object' || expected === null) &&
          (actual !== 0 || expected !== 0)) { // -0 === +0
        return `${kReadableOperator[operator]}\n\n` +
            `${actualLines[0]} !== ${expectedLines[0]}\n`;
      }
    } else if (operator !== 'strictEqualObject') {
      // If the stderr is a tty and the input length is lower than the current
      // columns per line, add a mismatch indicator below the output. If it is
      // not a tty, use a default value of 80 characters.
      const maxLength = process.stderr.isTTY ? process.stderr.columns : 80;
      if (inputLength < maxLength) {
        while (actualRaw[i] === expectedRaw[i]) {
          i++;
        }
        // Ignore the first characters.
        if (i > 2) {
          // Add position indicator for the first mismatch in case it is a
          // single line and the input length is less than the column length.
          indicator = `\n  ${StringPrototypeRepeat(' ', i)}^`;
          i = 0;
        }
      }
    }
  }

  // Remove all ending lines that match (this optimizes the output for
  // readability by reducing the number of total changed lines).
  let a = actualLines[actualLines.length - 1];
  let b = expectedLines[expectedLines.length - 1];
  while (a === b) {
    if (i++ < 3) {
      end = `\n  ${a}${end}`;
    } else {
      other = a;
    }
    ArrayPrototypePop(actualLines);
    ArrayPrototypePop(expectedLines);
    if (actualLines.length === 0 || expectedLines.length === 0)
      break;
    a = actualLines[actualLines.length - 1];
    b = expectedLines[expectedLines.length - 1];
  }

  const maxLines = MathMax(actualLines.length, expectedLines.length);
  // Strict equal with identical objects that are not identical by reference.
  // E.g., assert.deepStrictEqual({ a: Symbol() }, { a: Symbol() })
  if (maxLines === 0) {
    // We have to get the result again. The lines were all removed before.
    const actualLines = StringPrototypeSplit(actualInspected, '\n');

    // Only remove lines in case it makes sense to collapse those.
    // TODO: Accept env to always show the full error.
    if (actualLines.length > 50) {
      actualLines[46] = `${colors.blue}...${colors.white}`;
      while (actualLines.length > 47) {
        ArrayPrototypePop(actualLines);
      }
    }

    return `${kReadableOperator.notIdentical}\n\n` +
           `${ArrayPrototypeJoin(actualLines, '\n')}\n`;
  }

  // There were at least five identical lines at the end. Mark a couple of
  // skipped.
  if (i >= 5) {
    end = `\n${colors.blue}...${colors.white}${end}`;
    skipped = true;
  }
  if (other !== '') {
    end = `\n  ${other}${end}`;
    other = '';
  }

  let printedLines = 0;
  let identical = 0;
  const msg = kReadableOperator[operator] +
        `\n${colors.green}+ actual${colors.white} ${colors.red}- expected${colors.white}`;
  const skippedMsg = ` ${colors.blue}...${colors.white} Lines skipped`;

  let lines = actualLines;
  let plusMinus = `${colors.green}+${colors.white}`;
  let maxLength = expectedLines.length;
  if (actualLines.length < maxLines) {
    lines = expectedLines;
    plusMinus = `${colors.red}-${colors.white}`;
    maxLength = actualLines.length;
  }

  for (i = 0; i < maxLines; i++) {
    if (maxLength < i + 1) {
      // If more than two former lines are identical, print them. Collapse them
      // in case more than five lines were identical.
      if (identical > 2) {
        if (identical > 3) {
          if (identical > 4) {
            if (identical === 5) {
              res += `\n  ${lines[i - 3]}`;
              printedLines++;
            } else {
              res += `\n${colors.blue}...${colors.white}`;
              skipped = true;
            }
          }
          res += `\n  ${lines[i - 2]}`;
          printedLines++;
        }
        res += `\n  ${lines[i - 1]}`;
        printedLines++;
      }
      // No identical lines before.
      identical = 0;
      // Add the expected line to the cache.
      if (lines === actualLines) {
        res += `\n${plusMinus} ${lines[i]}`;
      } else {
        other += `\n${plusMinus} ${lines[i]}`;
      }
      printedLines++;
    // Only extra actual lines exist
    // Lines diverge
    } else {
      const expectedLine = expectedLines[i];
      let actualLine = actualLines[i];
      // If the lines diverge, specifically check for lines that only diverge by
      // a trailing comma. In that case it is actually identical and we should
      // mark it as such.
      let divergingLines =
        actualLine !== expectedLine &&
        (!StringPrototypeEndsWith(actualLine, ',') ||
         StringPrototypeSlice(actualLine, 0, -1) !== expectedLine);
      // If the expected line has a trailing comma but is otherwise identical,
      // add a comma at the end of the actual line. Otherwise the output could
      // look weird as in:
      //
      //   [
      //     1         // No comma at the end!
      // +   2
      //   ]
      //
      if (divergingLines &&
          StringPrototypeEndsWith(expectedLine, ',') &&
          StringPrototypeSlice(expectedLine, 0, -1) === actualLine) {
        divergingLines = false;
        actualLine += ',';
      }
      if (divergingLines) {
        // If more than two former lines are identical, print them. Collapse
        // them in case more than five lines were identical.
        if (identical > 2) {
          if (identical > 3) {
            if (identical > 4) {
              if (identical === 5) {
                res += `\n  ${actualLines[i - 3]}`;
                printedLines++;
              } else {
                res += `\n${colors.blue}...${colors.white}`;
                skipped = true;
              }
            }
            res += `\n  ${actualLines[i - 2]}`;
            printedLines++;
          }
          res += `\n  ${actualLines[i - 1]}`;
          printedLines++;
        }
        // No identical lines before.
        identical = 0;
        // Add the actual line to the result and cache the expected diverging
        // line so consecutive diverging lines show up as +++--- and not +-+-+-.
        res += `\n${colors.green}+${colors.white} ${actualLine}`;
        other += `\n${colors.red}-${colors.white} ${expectedLine}`;
        printedLines += 2;
      // Lines are identical
      } else {
        // Add all cached information to the result before adding other things
        // and reset the cache.
        res += other;
        other = '';
        identical++;
        // The very first identical line since the last diverging line is be
        // added to the result.
        if (identical <= 2) {
          res += `\n  ${actualLine}`;
          printedLines++;
        }
      }
    }
    // Inspected object to big (Show ~50 rows max)
    if (printedLines > 50 && i < maxLines - 2) {
      return `${msg}${skippedMsg}\n${res}\n${colors.blue}...${colors.white}${other}\n` +
             `${colors.blue}...${colors.white}`;
    }
  }

  return `${msg}${skipped ? skippedMsg : ''}\n${res}${other}${end}${indicator}`;
}

function addEllipsis(string) {
  const lines = StringPrototypeSplit(string, '\n', 11);
  if (lines.length > 10) {
    lines.length = 10;
    return `${ArrayPrototypeJoin(lines, '\n')}\n...`;
  } else if (string.length > 512) {
    return `${StringPrototypeSlice(string, 512)}...`;
  }
  return string;
}

class AssertionError extends Error {
  constructor(options) {
    validateObject(options, 'options');
    const {
      message,
      operator,
      stackStartFn,
      details,
      // Compatibility with older versions.
      stackStartFunction,
    } = options;
    let {
      actual,
      expected,
    } = options;

    const limit = Error.stackTraceLimit;
    if (isErrorStackTraceLimitWritable()) Error.stackTraceLimit = 0;

    if (message != null) {
      super(String(message));
    } else {
      // Reset colors on each call to make sure we handle dynamically set environment
      // variables correct.
      colors.refresh();
      // Prevent the error stack from being visible by duplicating the error
      // in a very close way to the original in case both sides are actually
      // instances of Error.
      if (typeof actual === 'object' && actual !== null &&
          typeof expected === 'object' && expected !== null &&
          'stack' in actual && actual instanceof Error &&
          'stack' in expected && expected instanceof Error) {
        actual = copyError(actual);
        expected = copyError(expected);
      }

      if (operator === 'deepStrictEqual' || operator === 'strictEqual') {
        super(createErrDiff(actual, expected, operator));
      } else if (operator === 'notDeepStrictEqual' ||
        operator === 'notStrictEqual') {
        // In case the objects are equal but the operator requires unequal, show
        // the first object and say A equals B
        let base = kReadableOperator[operator];
        const res = StringPrototypeSplit(inspectValue(actual), '\n');

        // In case "actual" is an object or a function, it should not be
        // reference equal.
        if (operator === 'notStrictEqual' &&
            ((typeof actual === 'object' && actual !== null) ||
             typeof actual === 'function')) {
          base = kReadableOperator.notStrictEqualObject;
        }

        // Only remove lines in case it makes sense to collapse those.
        // TODO: Accept env to always show the full error.
        if (res.length > 50) {
          res[46] = `${colors.blue}...${colors.white}`;
          while (res.length > 47) {
            ArrayPrototypePop(res);
          }
        }

        // Only print a single input.
        if (res.length === 1) {
          super(`${base}${res[0].length > 5 ? '\n\n' : ' '}${res[0]}`);
        } else {
          super(`${base}\n\n${ArrayPrototypeJoin(res, '\n')}\n`);
        }
      } else {
        let res = inspectValue(actual);
        let other = inspectValue(expected);
        const knownOperator = kReadableOperator[operator];
        if (operator === 'notDeepEqual' && res === other) {
          res = `${knownOperator}\n\n${res}`;
          if (res.length > 1024) {
            res = `${StringPrototypeSlice(res, 0, 1021)}...`;
          }
          super(res);
        } else {
          if (res.length > 512) {
            res = `${StringPrototypeSlice(res, 0, 509)}...`;
          }
          if (other.length > 512) {
            other = `${StringPrototypeSlice(other, 0, 509)}...`;
          }
          if (operator === 'deepEqual') {
            res = `${knownOperator}\n\n${res}\n\nshould loosely deep-equal\n\n`;
          } else {
            const newOp = kReadableOperator[`${operator}Unequal`];
            if (newOp) {
              res = `${newOp}\n\n${res}\n\nshould not loosely deep-equal\n\n`;
            } else {
              other = ` ${operator} ${other}`;
            }
          }
          super(`${res}${other}`);
        }
      }
    }

    if (isErrorStackTraceLimitWritable()) Error.stackTraceLimit = limit;

    this.generatedMessage = !message;
    ObjectDefineProperty(this, 'name', {
      __proto__: null,
      value: 'AssertionError [ERR_ASSERTION]',
      enumerable: false,
      writable: true,
      configurable: true,
    });
    this.code = 'ERR_ASSERTION';
    if (details) {
      this.actual = undefined;
      this.expected = undefined;
      this.operator = undefined;
      for (let i = 0; i < details.length; i++) {
        this['message ' + i] = details[i].message;
        this['actual ' + i] = details[i].actual;
        this['expected ' + i] = details[i].expected;
        this['operator ' + i] = details[i].operator;
        this['stack trace ' + i] = details[i].stack;
      }
    } else {
      this.actual = actual;
      this.expected = expected;
      this.operator = operator;
    }
    ErrorCaptureStackTrace(this, stackStartFn || stackStartFunction);
    // Create error message including the error code in the name.
    this.stack; // eslint-disable-line no-unused-expressions
    // Reset the name.
    this.name = 'AssertionError';
  }

  toString() {
    return `${this.name} [${this.code}]: ${this.message}`;
  }

  [inspect.custom](recurseTimes, ctx) {
    // Long strings should not be fully inspected.
    const tmpActual = this.actual;
    const tmpExpected = this.expected;

    if (typeof this.actual === 'string') {
      this.actual = addEllipsis(this.actual);
    }
    if (typeof this.expected === 'string') {
      this.expected = addEllipsis(this.expected);
    }

    // This limits the `actual` and `expected` property default inspection to
    // the minimum depth. Otherwise those values would be too verbose compared
    // to the actual error message which contains a combined view of these two
    // input values.
    const result = inspect(this, {
      ...ctx,
      customInspect: false,
      depth: 0,
    });

    // Reset the properties after inspection.
    this.actual = tmpActual;
    this.expected = tmpExpected;

    return result;
  }
}

module.exports = AssertionError;
