three.js/examples/jsm/modifiers/SubdivisionModifier.d.ts

import {
  BufferGeometry,
  Geometry
} from '../../../src/Three';

export class SubdivisionModifier {
  constructor(subdivisions?: number);
  subdivisions: number;
  
  modify(geometry: BufferGeometry | Geometry): Geometry;
  smooth(geometry: Geometry): void;
}