setZ( index, z ) {

		if ( this.normalized ) z = normalize( z, this.array );

		this.array[ index * this.itemSize + 2 ] = z;

		return this;

	}
Sets the z component of the vector at the given index.

@param {number} index - The index into the buffer attribute.
@param {number} z - The value to set.
@return {BufferAttribute} A reference to this instance.