SOLVED Get indexOf group on event

Questions
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1

SOLVED. Read https://threejs.org/docs/#api/en/core/Object3D.children

event.object returns!

Normally object.indexOf(event.target); returns a value. Not in that case.

dragControls.addEventListener( 'dragend', function (event) {
console.log(Array.from(group).indexOf(event.target)); 
}

returns -1

Heres my code:

var group = new THREE.Group();
var geometry = new THREE.CircleGeometry(10, 32);

// multiple times
var mesh = new THREE.Mesh(geometry, material);
group.add(mesh);

Anyone an idea how to get this childrens index in group?