Not checking checkbox event for javascript in ascx contro

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Javascript

checkbox

I have an ascx control in my application which has some checkboxes and checkboxlists.

I want to use javascript for doing some client side processing for these controls.
I have written the javasctript methods in a seperate file and am registering them through the code using Page.ClientScript.RegisterClientScriptBlock.
And the onclick event is subscribed by adding the attributes for onclick

UIControl.Attributes.Add("onchange", "SomeFunction();");

This seems to work fine for the checkbox list items .
But it doesnt work for checkboxes.

What could be going wrong here?
Thanks in advance.