Drag only on x and z axis

I want to translate an object on a plane and thus keep the position in whatever is the displacement for that I use the dragcontrols.js with this code:

dragControls.addEventListener ( 'drag', function( event ){
 event.object.position.y = 0; 

the object can move but moving up or down is very slow any idea ??

I also couldn’t get this to work but I’ve finally found a workaround. These steps require you to change DragControls.js:
Change the line:
_plane.setFromNormalAndCoplanarPoint( _camera.getWorldDirection( _plane.normal ), _worldPosition.setFromMatrixPosition( object.matrixWorld ) );
_plane.setFromNormalAndCoplanarPoint( {x: -10e-7, y: -1, z: 1e-7}, _worldPosition.setFromMatrixPosition( object.matrixWorld ) );

This change nothing for me … :frowning:
for information i’m using orthographic camera