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ただのメモ書き
ASP.NET側--------------------------------------------------------------------------
Private Sub Page_Load(略
Me.Response.ContentType = "application/json"
Me.Response.ContentEncoding = System.Text.Encoding.UTF8
Me.Response.Write("({""name"": ""いいえジョンです""})")
Me.Response.Flush()
Me.Response.Close()
End Sub

↓HTTP側--------------------------------------------------------------------------
//どっかで下記関数を呼び出す
function receiveJson(){
Utility.debugMode();
var url = "./ajaxtest.aspx?rows=true&searchString=1";
new Ajax.Request(url, {method: 'post', onComplete: receiveJsonComplete});
}

function receiveJsonComplete(httpObj){
Utility.degubWrite("responseJSON----------------------");
DisplayPropertyNames(httpObj.responseJSON);
Utility.degubWrite(httpObj.responseJSON.name);
}

function DisplayPropertyNames(obj){
var names = "";
for(var name in obj) names += name + " ";
Utility.degubWrite(names)
}

↓実行結果--------------------------------------------------------------------------
responseJSON----------------------
name
いいえジョンです