return 值是 undefined.Could 告诉我应该怎么做才能修复它？

Question

The value of store is undefined.colud tell me what I did wrong. Should I use Async and await or Promise ?

var store = db.read(collectionName, (status, data) => {
        //database read function
        if (status) {
          names.listOfData = data;
          var send = names;
          console.log("send---->", send);     // send value here is what I need to return.
          return send;            // Getting required data for send. Problem here is returning it and storing it in store.
        } else {
          return null;
        }
      });

console.log("store-->", store);

Here value of store is Undefined. No proper return

Answer 1

您无法写入要存储的结果并在 db.read 之后立即看到它，因为 db.read 不会等待回调完成并且不会 return 来自它作为 return 值。

您应该将此调用包装到 new Promise。它可能看起来像这样：

var store = await (new Promise(resolve, reject) => {
  db.read(collectionName, (status, data) => {
        //database read function
        if (status) {
          names.listOfData = data;
          var send = names;
          console.log("send---->", send);     // send value here is what I need to return.
          resolve(send);
        } else {
          resolve(null);
        }
      });
});

请阅读有关异步函数的更多信息，async/await、Promise 以及如何将带有回调的函数转换为异步函数。

return 值是 undefined.Could 告诉我应该怎么做才能修复它？

The return value is undefined.Could tell what should I do to fix it?

javascript

asynchronous

mongodb

typescript

mean-stack