three.js smooth normals with crease angle

computeVertexNormals-angle.js

function calcNormal( normals, normal, angle ){
	let allowed = normals.filter( n => n.angleTo( normal ) < angle * Math.PI / 180 );
	
	return allowed.reduce( (a, b) => a.clone().add( b ) ).normalize();
}

THREE.GeometryUtils.computeVertexNormals = function(geometry, angle){
	geometry.computeFaceNormals();
	
	var vertices = geometry.vertices.map( () => [] ); // vertices with normals array

	geometry.faces.map( face => {
		vertices[ face.a ].push( face.normal );
		vertices[ face.b ].push( face.normal );
		vertices[ face.c ].push( face.normal );
	});

	geometry.faces.map( face => {
		face.vertexNormals[ 0 ] = calcNormal( vertices[ face.a ], face.normal, angle );
		face.vertexNormals[ 1 ] = calcNormal( vertices[ face.b ], face.normal, angle );
		face.vertexNormals[ 2 ] = calcNormal( vertices[ face.c ], face.normal, angle );
	});

	if ( geometry.faces.length > 0 ) 
		geometry.normalsNeedUpdate = true;
}

@xaliphostes nope, didn't work on that.
Maybe you can find some links in mrdoob/three.js#14859