get item id using javascript after commit

hi friends

i am using below code to for custom save button.

<input class="ms-btn" id="btnApp" onclick="javascript: {ddwrt:GenFireServerEvent('__commit')}; AfterSave();" type="button" value="Approve" />

my problem is i need to get item id in AfterSave() function

using "var itemId= _spPageContextInfo.pageItemId;" am not getting

is there any way to get the id of item.