FileSystemAccessAPIを使ってJSONの読み書きをする

LocalFileJsonRepository.js

class LocalFileJsonRepository {
  constructor(fileHandle = null) {
    this.fileHandle = fileHandle;
  }
  async init() {
    if(this.fileHandle) {
      return;
    }
    [this.fileHandle] = await window.showOpenFilePicker();
  }
  async load() {
    const file = await this.fileHandle.getFile();
    const text = await file.text();

    return JSON.parse(text);
  }
  async save(obj) {
    const writable = await this.fileHandle.createWritable();
    await writable.write(JSON.stringify(obj));
    await writable.close();
  }
  close() {
    this.fileHandle = null;
  }
}