changing text in asp:button using javascript

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ASP.NET

Javascript

Hello, I would like to change the value using javascript in a asp:button to catch the value on the code behind when i click on it, the default value Text="show"

i see the change on the page when i use the javascript "left: ......."
but when i catch the button in code behind with string a = button.text i get the default value "show" and not the value shown on the button on the webpage.

this is the javascript code that changes the text on the button

document.getElementById("hidden1").text = ("Left: " + $(this).parent().dialog('widget').position().left + " Top: " + $(this).parent().dialog('widget').position().top);

// click the button
document.getElementById("hidden1").click();

Also i don't want to reload the page when the button i clicked, i only want to catch the value in the button from code behind, can ajax solve this?

Can anyone help, Thanks