MongoDB using with NodeJS - mongodb

Question

I want to connect mongodb to nodejs.
I succeed to connect mongodb to nodejs but I can't access to mongodb Collection (test collection).
How can I use collection in my code?
BELOW MY CODE
var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/test';
var db;
MongoClient.connect(url, function (err, database) {
if (err) {
console.error('MongoDB 연결 실패', err);
return;
}else{
console.log("DB연결 성공")
}
db = database;
});
var movies = db.Collection('test');
movies.insert();
ERROR CODE
TypeError: Cannot read properties of undefined (reading 'Collection')
at Object.<anonymous> (C:\Users\USER\Desktop\test\mongodbtest.js:15:17)
at Module._compile (node:internal/modules/cjs/loader:1126:14)
at Object.Module._extensions..js (node:internal/modules/cjs/loader:1180:10)
at Module.load (node:internal/modules/cjs/loader:1004:32)
at Function.Module._load (node:internal/modules/cjs/loader:839:12)
at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
at node:internal/main/run_main_module:17:47

Answer 1

You are trying to access the db instance sequentially, but the code in the callback will be executed after the var movies = db.Collection('test'); line is called, so the variable won't be set.
You can either move the insert inside the callback:
var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/test';
MongoClient.connect(url, function (err, database) {
if (err) {
console.error('MongoDB 연결 실패', err);
return;
} else {
console.log('DB연결 성공');
}
var movies = database.Collection('test');
movies.insert();
});
Or use async await:
var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/test';
const connectDb = async () => {
try {
return await MongoClient.connect(url)
} catch (err) {
console.error('MongoDB 연결 실패', err);
}
}
connectDb()
.then((db) => {
var movies = db.Collection('test');
movies.insert();
})