获取数据

基本思想：

• 连接某个数据库
• get 数据
• 请求发出后立即异步，监听 onerror 和 onsuccess
• 请求成功后处理数据

window.indexedDB =
  window.indexedDB ||
  window.webkitIndexedDB ||
  window.mozIndexedDB ||
  window.msIndexedDB;
window.IDBTransaction =
  window.IDBTransaction ||
  window.webkitIDBTransaction ||
  window.msIDBTransaction;
window.IDBKeyRange =
  window.IDBKeyRange || window.webkitIDBKeyRange || window.msIDBKeyRange;
window.IDBCursor =
  window.IDBCursor || window.webkitIDBCursor || window.msIDBCursor;
function getData() {
  var dbName = 'indexedDBTest'; // 数据库名
  var dbVersion = 20220430; // 版本号
  var idb;
  var dbConnect = indexedDB.open(dbName, dbVersion);
  dbConnect.onsuccess = function (e) {
    idb = e.target.result;
    var t = idb.transaction(['users'], 'readonly');
    var s = t.objectStore('users');
    var r = s.get(1);
    r.onsuccess = function (e) {
      if (this.result == undefined) console.log('没有符合的数据');
      else console.log('数据获取成功，用户名为：' + this.result.userName);
    };
    r.onerror = function (e) {
      console.log('数据获取失败');
    };
  };
  dbConnect.onerror = function (e) {
    console.log('连接 indexedDB 数据库失败');
  };
}