How to flip normal in BufferGeometry?

Questions
,
1

How to flip normal in BufferGeometry? current normal is from inside to outside, I want to flip that.

var geometry = new THREE.BufferGeometry(); 

var vertices = new Float32Array([
  0, 0, 0,
  80, 0, 0, 
  80, 80, 0, 
  0, 80, 0, 
]);

var attribue = new THREE.BufferAttribute(vertices, 3);

geometry.attributes.position = attribue
var normals = new Float32Array([
  0, 0, 1, 
  0, 0, 1, 
  0, 0, 1,
  0, 0, 1,
]);

geometry.attributes.normal = new THREE.BufferAttribute(normals, 3); 

var indexes = new Uint16Array([
  0, 1, 2, 0, 2, 3,
])

geometry.index = new THREE.BufferAttribute(indexes, 1);

 var uvs = new Float32Array([
   0,0, 
   1,0,
   1,1,
   0,1, 
 ]);
 
 geometry.attributes.uv = new THREE.BufferAttribute(uvs, 2);
2

I found the answer here.

geom.applyMatrix4(new Matrix4().makeScale(-1, 1, 1));//flip the normals

    let temp;
    for ( let i = 0; i < geometry.index.array.length; i += 3 ) {
      // swap the first and third values
      temp = geometry.index.array[ i ];
      geometry.index.array[ i ] = geometry.index.array[ i + 2 ];
      geometry.index.array[ i + 2 ] = temp;
    }