使用 Promises 迭代删除 IndexedDb 中的项目

Question

我对这里的 promises 有点陌生，所以解决方案可能是微不足道的/语法上的。

我在存储媒体时的目标是查看是否设置了配额，并且 - 如果需要 - 从 store 删除项目直到我们有空间。

我的尝试在这里，但我最大的痛点是while循环——弄清楚如何等到一个项目被删除后重新评估是否继续删除：

   const store = database.transaction(storeName, "readwrite").objectStore(storeName);
   while (storageUsedInGb > storageQuotaInGb) {
       // problem: pause loop here
       const latestMediaRequest = store.get(latestMediaGuid);
       latestMediaRequest.onsuccess = function(event) {
              var deleteRequest = store.delete(latestMediaGuid);
              deleteRequest.onsuccess = function () {
                    storageUsedInGb -= event.target.media.size / 1024 / 1000 / 1000;
                       // problem: continue loop here
              }
              deleteRequest.onerror = reject;
        }
        latestMediaRequest.onerror = reject;
    }

如何告诉 while 循环等待迭代，直到我从 latestMediaRequest 和 deleteRequest 得到解决方案（更新 storageUsedInGb）？

Answer 1

您可以使用递归调用的函数进行异步循环。该函数可以是立即调用的函数表达式：

const store = database.transaction(storeName, "readwrite").objectStore(storeName);
(function loop(storageUsedInGb) {
    if (storageUsedInGb <= storageQuotaInGb) {
        // if you are in a promise constructor callback, you will call resolve() here
        return; // exit chain of loop calls
    }
    const latestMediaRequest = store.get(latestMediaGuid);
    latestMediaRequest.onsuccess = function(event) {
        var deleteRequest = store.delete(latestMediaGuid);
        deleteRequest.onsuccess = 
            loop.bind(null, storageUsedInGb-event.target.media.size / 1024 / 1000 / 1000);
        deleteRequest.onerror = reject;
    }
    latestMediaRequest.onerror = reject;
})(storageUsedInGb); // call immediately