How can i retrieve current record guid in java script.

Hello,

I'm  saveing my entity record using Xrm.Page.data.entity.save(); using javascript.
next line I want to retrive my current save record guid using 

Xrm.Page.data.entity.getId() .

It is giving me null value.

Please help me

How can i retrieve current record guid in java script.

Thanks 
Kashyap Diwan