how do i access form field values across windows?

To access the contents of a form field in new window from the original window:
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var myVar =newwin.document.formName.formFieldName.value;

To access the contents of a form field in the original window from the new window:try the followong code.
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var myVar = opener.document.formName.formFieldName.value;

To access the contents of a form field in the original window from a frame in the new window:
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var myVar = top.opener.document.formName.formFieldName.value;