sharepoint 2013 application page while using javascript client object model added script link tags.

when used onDeman=true my code started working.

 <SharePoint:ScriptLink ID="ScriptLink1" language="javascript"  OnDemand="true" Name="SP.js" defer="true" runat="server" Localizable="false"/>
    <SharePoint:ScriptLink ID="ScriptLink2" language="javascript" name="SP.Debug.js" defer="true" runat="server" Localizable="false"/>
    <SharePoint:ScriptLink ID="ScriptLink3" language="javascript"  OnDemand="true" Name="SP.Runtime.Debug.js" defer="true" runat="server" Localizable="false"/>
    <SharePoint:ScriptLink ID="ScriptLink4" language="javascript"  OnDemand="true" Name="SP.core.js" defer="true" runat="server" Localizable="false"/>