function Form2Popup(params, actionUrl, name, popupConfig, get) { 
        // free in choice: post or get
        var method = (get == undefined || !get) ? 'POST' : 'GET'; 
 
        // it's important to assign non-null name!
        if (name == undefined || name == '') { 
                name = 'tmpPopup'; 
        } 
        var form = document.createElement('<form action="' + actionUrl + '" method="' + method + '" target="' + name + '" style="display:none;"></form>'); 
        var element = null; 
        for (var propName in params) { 
                element = document.createElement('<input type="text" name="' + propName + '" value="' + params[propName] + '">'); 
                form.appendChild(element); 
        } 
        document.body.appendChild(form);
 
        // First, open empty window: why make redundant request to server?
        var win = window.open('about:blank', name, popupConfig); 
 
        // in order to restore this window
        // if it's already been opened before
        win.focus(); 
        form.submit();
        form.removeNode(true); 
        return win; 
}
 
.......
// Example:
var _name = document.getElementById("nameDiv");
var _text = forms['myform'].messageTextarea.value;
var params = {name:_name,title:"user preview",txt:_text};
 
var previewPopup = Form2Popup(params, 'save.jsp?preview=1', 'preview', 'top=100,left=100,scrollbars=1');