JavaScript の yield で非同期なコードを動機っぽく書く例

gistfile1.js

// based on http://labs.cybozu.co.jp/blog/kazuho/archives/2007/05/coopthread.php
function get_all(urls) {
  runnable(function (next) {
    for (var i = 0; i < urls.length; i++) {
      // build request
      var xhr = new XMLHttpRequest();
      xhr.open("get", urls[i], true);
      xhr.onreadystatechange = function () {
        if (xhr.readyState == 4)
          next(xhr.responseText);
      };
      xhr.send(null);
      // handle response
      var responseText = yield;
    }
  });
}