Why this button doesn't cause triple postback?

Question

We have developed a page with a asp.net and debugging it accidentally we have discovered on our page button with the next code on onclik attribute

onclick="__doPostBack('ctl00$FormPlace$m_userTaskMarkAsUnreadButton',''); __doPostBack('ctl00$FormPlace$m_userTaskMarkAsUnreadButton','');WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions("ctl00$FormPlace$m_userTaskMarkAsUnreadButton", "", true, "", "", false, false))"

It seems that the button do three postbacks but when we click it only cause on postback. With this code seems that de button will cause three postbacks!!

We have try it with Internet Explorer and Firefox and the button only cause on postback always. Are browsers who avoid that the button do three postback ? Or Is Asp.net server who avoid the three postback? We don't understand why the button behaves correctly if onclick attribute has three call to do Postbacks.

Thanks

Answer 1

If the first JavaScript function called causes the page to POST your data (not using an XMLHttpRequest), a new page is loaded and the execution of your JavaScript stops.

Answer 2

The first __doPostback will post the page immediately. The remaining two statements will never be executed.