ES6 : How to export this variable of node.js? - node.js

Question

There is a piece of code that querying data from mongodb with node.js:
var MongoClient = require('mongodb').MongoClient
, assert = require('assert');
//a query that returns all the documents
var findDocuments = function(db, callback) {
// Get the documents collection
var collection = db.collection('documents');
// Find some documents
collection.find({}).toArray(function(err, docs) {
assert.equal(err, null);
console.log("Found the following records");
console.log(docs)
callback(docs);
});
}
var MongoClient = require('mongodb').MongoClient
, assert = require('assert');
// Connection URL
var url = 'mongodb://localhost:27017/myproject';
// Use connect method to connect to the server
MongoClient.connect(url, function(err, db) {
assert.equal(null, err);
console.log("Connected correctly to server");
var result = findDocuments(db, function() {
db.close();
});
});
//export the query result,but it doesn't work because it is a local variable in `MongoClient.connect()`
export {result}
Question:
I want to export the variable result, but it doesn't work because it is a local variable in MongoClient.connect().What should I do?

Answer 1

Define it outside the function like
var result

Answer 2

You need to define it globally in the document.
var MongoClient = require('mongodb').MongoClient
, assert = require('assert');
var result; //define it out here to be able to use it on anywhere
//a query that returns all the documents
var findDocuments = function(db, callback) {
// Get the documents collection
var collection = db.collection('documents');
// Find some documents
collection.find({}).toArray(function(err, docs) {
assert.equal(err, null);
console.log("Found the following records");
console.log(docs)
callback(docs);
});
}
var MongoClient = require('mongodb').MongoClient
, assert = require('assert');
// Connection URL
var url = 'mongodb://localhost:27017/myproject';
// Use connect method to connect to the server
MongoClient.connect(url, function(err, db) {
assert.equal(null, err);
console.log("Connected correctly to server");
result = findDocuments(db, function() { //give it its value
db.close();
});
});
//export the query result,but it doesn't work because it is a local variable in `MongoClient.connect()`
export {result}

Answer 3

If you are using ES6, I would recommend to use the keywords let/const instead of var.
Now about your issue why would you export result that way?
You should create a function connect() and export it. Then in your controller, call this function and handle whatever the outcome is.
Your connect here is totally asynchronous and uncontrolled, which is very bad behavior.
Exemple of what to do :
file mongodb.es6
export default class Mongodb {
connect() {
...
}
...
}
file main.es6
const mongodbObject = new Mongodb();
mongodbObject.connect()
.then(() => {
// I am connected so I can do whatever I want
})
.catch((err) => {
// I have an error and do something about it
});

Answer 4

Don't do it like this!
This will ONLY query the data when the file is being executed. I don't see any reason to do it this way.
Instead expose a function from this file, which will connect to the DB, query it and return the result object, everytime you call it.
export {
getResult: function(query, callback) {
// Connection URL
var url = 'mongodb://localhost:27017/myproject';
// Use connect method to connect to the server
MongoClient.connect(url, function(err, db) {
if (err) return callback(err);
console.log("Connected correctly to server");
result = findDocuments(db, function() {
db.close();
});
callback(null, result);
});
}
}