IndexedDB 成功与不需要的比赛

Question

我用新版本号打开 indexedDB

var R = indexedDB.open("myDB", 2); // <- new version
R.onupgradeneeded = longRunningFunction;
R.onsuccess = longRunningFunction2;

现在我需要在两个运行ning 长函数完成后运行一个函数。哪种代码模式适用于此？

Answer 1

使用承诺或回调。等待成功事件触发，完成它的工作，然后解决承诺或调用回调。然后你可以在承诺解决后或回调被调用时做一些事情。

编辑，这是一个粗略的例子：

function myOpenIndexedDB(name, version, onupgradeneeded) {
  return new Promise((resolve, reject) => {
    var request = indexedDB.open(name, version);
    request.onupgradeneeded = onupgradeneeded;
    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });  
}

function myOnUpgradeNeeded(event) {
  console.log('Performing database upgrade');
  const openRequest = event.target;

  // just to demonstrate
  const versionChangeTransaction = openRequest.transaction;
  versionChangeTransaction.oncomplete = () => {
    console.log('The version change transaction completed ' + 
      'which basically means the upgradeneeded handler completed');
  };
}

async function main() {
  console.log('Connecting to database');
  const indexedDbConn = await myOpenIndexedDB('myDb', 2, myOnUpgradeNeeded);
  console.log('Connected to database', indexedDbConn.name);

  // Do more stuff
  await runSomeQuery(indexedDbConn);
}

// Run the example
main().catch(console.error);

引用次数

有关详细信息，请参阅

中突出显示的浅绿色块

https://www.w3.org/TR/IndexedDB/#upgrade-transaction-construct
https://www.w3.org/TR/IndexedDB/#factory-interface 第 6 步和第 7 步

IndexedDB 成功与不需要的比赛

IndexedDB success vs ungradeneeded race

javascript

concurrency

event-handling

indexeddb

引用次数