变量 scope 错误时尝试 JSON.stringify object 在存储所述 ZA8CFDE6331BD59EB2AC96F891ZB4 之后

Question

Firstly, I would like to address my situation. I am attempting to build a to-do list webapp, in which I save my tasks in a MongoDB, so that I can pull the tasks from the MongoDB so that on the front end the task remains there permanently. The problem is, when I try to convert the object containing the task into a string, so that I can reference it in my client side JS, I get variable scope error (I am assuming) where the object is undefined, and thus I cannot res.end the data to my script.js file. Here is the code

app.get("/tasks", (req, res) => {
  console.log(req.query.task)
  res.send("hi " + req.query.task)
  MongoClient.connect(url, function(err, db) {
    if (err) throw err
    var dbo = db.db("Cluster0")
    
    var myobj = { task: req.query.task }
    
    dbo.collection("articles").insertOne(myobj, function(err, res) {
     
      if (err) throw err
      console.log("1 document inserted")
      db.close();
      
    })
        var data = JSON.stringify(myobj)

    res.end(data);
    console.log(myobj)
    /*dbo.collection("articles").deleteMany({}, function(err, obj) {
      if (err) throw err;
      console.log(obj.result.n + " document(s) deleted");
      db.close();
    });*/




  })
  
    
})

Here are my errors

ReferenceError: myobj is not defined
    at /home/runner/todolist/index.js:43:29
    at Layer.handle [as handle_request] (/home/runner/todolist/node_modules/express/lib/router/layer.js:95:5)
    at next (/home/runner/todolist/node_modules/express/lib/router/route.js:137:13)
    at Route.dispatch (/home/runner/todolist/node_modules/express/lib/router/route.js:112:3)
    at Layer.handle [as handle_request] (/home/runner/todolist/node_modules/express/lib/router/layer.js:95:5)
    at /home/runner/todolist/node_modules/express/lib/router/index.js:281:22
    at Function.process_params (/home/runner/todolist/node_modules/express/lib/router/index.js:335:12)
    at next (/home/runner/todolist/node_modules/express/lib/router/index.js:275:10)
    at expressInit (/home/runner/todolist/node_modules/express/lib/middleware/init.js:40:5)
    at Layer.handle [as handle_request] (/home/runner/todolist/node_modules/express/lib/router/layer.js:95:5)
(node:7548) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
{ task: 'sadsda', _id: 5efbe175fef3df1d7c5135ce }
1 document inserted
 

As you can see, I can indeed console.log(myobj), so I am not sure why it is not able to be converted with JSON.stringify. On a side note, if I am able to successfully parse the object into my client side JS file, will the information stay their permanently, or will it be gone if I refresh the webpage? Any ideas on how I can directly take out data from my MongoDB and store the info in my client side JS so that I can display the To-do tasks permanently? I hope I am making myself specific.

Answer 1

When you insert myobj , make sure you also then return it, send to client once successfuly saved and then display it however you want:

db.collection('articles').insertOne(myobj, function (error, response) {
    if(error) {
        console.log('Error occurred while inserting');
    } else {
       console.log('inserted record', response.ops[0]);
       //send if saved obj is returned
       res.send(response.ops[0])
    }
});

---

The information will be always refreshed on a client-side (page refresh). You will need to make the call again to grab relevant information from the database. Of course, you could try to save some information in cookies but that would be an overkill in this case.

In general, it would be ok to do one request to get the list each time client visits the page.

---

You only use myobj to save it to your database. After that, you should work with the response from the insertOne - newly saved document.

It might be the case that saving the data to the database was not successful - in that case, you do not want to send the object anyway (will be misleading).

For your reference - ops Contains the documents inserted with added _id fields

response.ops is going to be an array so we need to access the first element of it at an index of 0 - [0]

I do not think you necessarily need to use JSON.stringify on the backend in this case. See what works best for you.