three.js/src/animation/PropertyMixer.d.ts

export class PropertyMixer {
  constructor(binding: any, typeName: string, valueSize: number);

  binding: any;
  valueSize: number;
  buffer: any;
  cumulativeWeight: number;
  useCount: number;
  referenceCount: number;

  accumulate(accuIndex: number, weight: number): void;
  apply(accuIndex: number): void;
  saveOriginalState(): void;
  restoreOriginalState(): void;
}