Question

我对这里的承诺有点新意，所以解决方案可能很简单/语法化。

存储媒体的目的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。

我的尝试就在这里，但我最大的痛点是while循环 - 弄清楚如何等到项目被删除以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;
    }

我怎么能告诉while循环等待迭代，直到我得到latestMediaRequest然后deleteRequest（更新storageUsedInGb）的分辨率？

Answer 1

您可以使用递归调用的函数进行异步循环。该函数可以是一个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

使用Promise迭代删除IndexedDb中的项目

1 个答案: