Date format change

Hi I try to change date format but I am not able to change..
Please help me.
I need required format is 'yyyy - MM - dd' instead of 'Sat Nov 14 2015 00:00:00 GMT+0530 (IST)'

I try to change this way but not working.

<button class="button button-block button-calm item-positive" >Date :
        {{datepickerObject.inputDate | date:'yyyy - MM - dd'}}</button>

Thanks..
