我试过了

• https://www.tutorialspoint.com/execute_dart_online.php
• https://www.jdoodle.com/execute-dart-online

无法重现该问题，但dartpad会抛出错误。

import 'dart:io';

main() {
    sleep(const Duration(seconds:1));
    print('This will be logged to the console in the browser.');
}

结果：

$dart main.dart
This will be logged to the console in the browser.

DartPad上的错误看起来像睡眠错误：

wrapException
_ProcessUtils__sleep
main
<anonymous>
<anonymous>
<anonymous>
<anonymous>
replaceJavaScript
messageHandler/<

然而，使用睡眠这种方式不会打破DartPad。

import 'dart:async';

Future sleep1() {
  return new Future.delayed(const Duration(seconds: 1), () => "1");
}

main() {
    sleep1();
    print('This will be logged to the console in the browser.');
}