节点和expressjs中快速路由器方法调用和module.export方法调用和app.use（）调用之间的区别

Question

i have app.js which have

var express = require('express');
var report = require('./routes/Report');

var app = express();

app.use('/api/appReport', report);

app.listen(3000);
module.exports = app;

i have Report.js

var express = require('express');
var router = express.Router();

var reportDb = require('../db/ReportDB');

reportDb.test(function(res) {
});

router.get('/all', function(req, resp) {
    reportDb.getAll(function(result) {
        resp.status(200);
        resp.send(result);
        return resp;
    });

}); 

i have ReportDB.js

module.exports.test = function() {
    console.log('Hello');
}

module.exports.getAll = function (callback) {
    //Some operations
};

the above code are working fine.

My question is

when i start the node js server it is automatically calling reportDb.test() present in Report.js but it is not automatically calling router.get() present in Report.js. so i want to know what is the difference on calling of test() and router.get() ?

i know when we hit '/all' url then it will call router.get(). but for reportDb.test() we are not calling in app.js, so how it is automatically calling at the time of server starting ?

let say if i use below function inside Report.js. then it'll not exicute.

function test1() {
    console.log('hello...');
}

i want to know is it app.use() calls all the method automatically which are exported ?

Answer 1

Its calling test() because you have written

    reportDb.test(function(res) {

    });

in report.js and included reportDb.js in it. Also you have included report.js in app.js.

    app.use('/api/appReport', report);

Its not that calling test()

Your router.get() will call when you will hit the url like localhost:3000/all