如何在Node.js＆Express中使用全局变量（可共享变量）

Question

I have a file called data.js for keeping data as memory database.

var express = require('express');
var app = express();

var aList;
var bList;
var cList;

module.exports = app;

And I want to initialise data when I start the server. So, I implemented init() in app.js

...
var data = require('./data'); // data.js is located in the same folder.

app.set(...);
app.use(...);
...

init();

...

});

fun init(){
    console.log("Hello!");

    aList = getDumpDataList(10); // I also tried with 'data.aList = getDumpDataList(10);' but didn't work.

    console.log(JSON.stringify(aList));
}

fun getDumpDataList(n){
    var list;

    ... // for loop to generate random elements.

    return list;
}

module.exports = app;

When I printed with console.log() , Hello! is printed but aList isn't printed but undefined

And I also want to use the data in routers under routes folder.

So, what I did is.

...
var data = require('./data');

route.get("/...", function(req, res, next){
    console.log(JSON.stringify(aList));
    ...
});

But it is also undefined .

I am just making simple test server that initialise data whenever I re-run.

How can I share variables between the js files?

Answer 1

You do not export those vars:

const express = require('express');
const app = express();

let aList;
let bList;
let cList;

module.exports.app = app;
module.exports.aList = aList;
module.exports.bList = bList;
module.exports.cList = cList;

• ...but i would not put express in data.js , rather put it in app.js .
• I would also initialize those vars with initial values in data.js , if the initial data does not depend on something else.
• Last but not least: Do not use var anymore, use let and const instead. It is supported since Node 6+ ( https://node.green/ ). I replaced it in the code.