Flip Selection

app.activeDocument.flipCanvas(Direction.HORIZONTAL);
app.activeDocument.flipCanvas(Direction.VERTICAL);

If there is a cleaner way please post but this does it via scriptListener, pass "v" or "h" to the function:

function flipSelection(direction){
var dir = "Vrtc"
if(direction=="h"){
dir="Hrzn"
}
var id17 = charIDToTypeID( "Flip" );
var desc4 = new ActionDescriptor();
var id18 = charIDToTypeID( "null" );
var ref2 = new ActionReference();
var id19 = charIDToTypeID( "Lyr " );
var id20 = charIDToTypeID( "Ordn" );
var id21 = charIDToTypeID( "Trgt" );
ref2.putEnumerated( id19, id20, id21 );
desc4.putReference( id18, ref2 );
var id22 = charIDToTypeID( "Axis" );
var id23 = charIDToTypeID( "Ornt" );
var id24 = charIDToTypeID( dir );
desc4.putEnumerated( id22, id23, id24 );
executeAction( id17, desc4, DialogModes.NO );
}