need help urgently

Hi all,
I am new to JavaScript. i am making a page which shoud have a div floating. i changed the position to fixed which solved it but now i want to change the position to the absolute on condition that when the scrolling div comes to a certain area i can change it is that consider the code

Code:

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<div id="container" >
<DIV id="formButtons"><asp:Button id="Button1" onclick="Button1_Click" runat="server" BackColor="Aqua" Width="201px" Text="Save Form"></asp:Button> </DIV></div>

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the div container is the parent div with height 500px and div formButtons is the scrolling div
i want scroling div to move in the parent div is that if i scroll to the bottom the scrolling div should stick on the bottom of the container div
the javascript i used for this is as follows it works but the problem is i am using constant values it will work if the window is of specific size is there any way to get the end position of the parent div

Code:

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window.onscroll = function()
    {
           
                   
                    if (document.documentElement.scrollTop < "530") //the value i have putten in quatation is the constant where i need a certain function to dynamicaly get the values the value entered here is one where i want div to stick but it changes when maximized
                    {
                           
                          document.getElementById("formButtons").style.position= 'fixed';
                          document.getElementById("formButtons").style.bottom= '0px';
                          document.getElementById("formButtons").style.right= '0px';
                         
                    }
                    else
                    {
                        document.getElementById("formButtons").style.position='absolute';
                            document.getElementById("formButtons").style.right='0px';
                            document.getElementById("formButtons").style.bottom="'-690px'"; the value here should also be assigned dynamically on parent container bottom right
                         
                         
                    }
               
        }

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what should i do please Help?

I'm sorry, but I am having a difficult time understanding your English.

Can't you just add the start y coordinate of your div to the height of the div? That will give you the exact y coordinate of the botton of the div.

Code:

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var obj = document.getElementById('YOUR_DIV_ID');
if (obj.offsetParent) {
  var y = obj.offsetTop;
  var h = obj.offsetHeight;
  while (obj = obj.offsetParent) {
    y += obj.offsetTop;
  }
}
var bottom = y + h;

alert(bottom); // this should return the bottom y coordinate of your div

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