如何修改沙箱路径下json文件的指定内容

import { fileIo } from '@kit.CoreFileKit'; 
 
let basePath = "/test.txt";  
let sanFile = fileIo.openSync(basePath, fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.CREATE); 
let fd = sanFile.fd;

let length: number = 4096; 
let arrayBuffer = new ArrayBuffer(length); 
let content = fileIo.readSync(fd, arrayBuffer);

obj.name = 'new name';

fileIo.writeSync(fd, JSON.stringify(obj));