PostBack Handling Java Script

Question

I am displaying a popup in using java script. It is Working fine if Post back is not there. On page Post back the PopUp position getting changed. But on page post back also i want the code to be workd fine. the code id

var object = this.doc.getElementById('lbMain'); object.style.top = (this.getPageScroll() + (pageSize[3] / 15)) + "px"; object.style.display = '';

Please help me on this