extensions/typescript-language-features/src/tsServer/bufferSyncSupport.ts/SyncedBuffer/kind
class SyncedBuffer:	public get kind(): BufferKind {
		switch (this.document.languageId) {
			case languageModeIds.javascript:
			case languageModeIds.javascriptreact:
				return BufferKind.JavaScript;

			case languageModeIds.typescript:
			case languageModeIds.typescriptreact:
			default:
				return BufferKind.TypeScript;
		}
	}