<input type="date" id="a">

<script>
this.toDateInput = Symbol( 'czNic::Date' );
Date.prototype[ this.toDateInput ] = function ()
{
  return new Date( this.getTime() - ( this.getTimezoneOffset() * 60000 ) ).toISOString().split( 'T' )[ 0 ];
};
const b = new Date();
document.getElementById('a').value = b[ this.toDateInput ]();
</script>