demo/module-import/js/vendor/GLTFLoader.js
function GLTFDracoMeshCompressionExtension( json, dracoLoader ) {

  if ( !dracoLoader ) {

    throw new Error( 'THREE.GLTFLoader: No DRACOLoader instance provided.' );

  }

  this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION;
  this.json = json;
  this.dracoLoader = dracoLoader;
  THREE.DRACOLoader.getDecoderModule();

}
function GLTFDracoMeshCompressionExtension( json, dracoLoader ) {

  if ( !dracoLoader ) {

    throw new Error( 'THREE.GLTFLoader: No DRACOLoader instance provided.' );

  }

  this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION;
  this.json = json;
  this.dracoLoader = dracoLoader;
  THREE.DRACOLoader.getDecoderModule();

}
function GLTFDracoMeshCompressionExtension ( json , dracoLoader ) { if ( ! dracoLoader ) { throw new Error ( 'THREE.GLTFLoader: No DRACOLoader instance provided.' ) ; } this . name = EXTENSIONS . KHR_DRACO_MESH_COMPRESSION ; this . json = json ; this . dracoLoader = dracoLoader ; THREE . DRACOLoader . getDecoderModule ( ) ; }
DRACO Mesh Compression Extension

Specification: https://github.com/KhronosGroup/glTF/pull/874
DRACO Mesh Compression Extension