■サンプルソース

ダメな例

var request = createHttpRequest();//XMLHttpRequestの生成
request.open("POST","●●●");
request.send("");
request.onreadystatechange = callbackFunction;

こうすればOK

var request = createHttpRequest();//XMLHttpRequestの生成
request.onreadystatechange = callbackFunction;
request.open("POST","●●●");
request.send("");