node.js : function.prototype.method multiple exports inside one file

user_12129118 0
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Noob in JS here.

Let's say I have a js file where the contents are like

function a(){}
a.prototype.method1 = function() { ... };
a.prototype.method2 = function() { ... };

function b(){}
b.prototype.method3 = function() { ... };
b.prototype.method4 = function() { ... };

module.exports = new a();
module.exports = new b();

In this file, I've function definition. In the next file, I'm trying to access the methods below

var x = require('./file.js');

x.a.method1();   //Not working
x.method1();     //Not working

But both types of accessing result in error for me. Can you please help me with steps on how to access the methods correctly?

And I can access those functions if I try to have only 1 export in one file. But I want it to be like this. 2 exports in a same file.

node.js javascript
2 Answers

The problem is that you're replacing the exports property twice:

module.exports = new a();
module.exports = new b();

As a result, you're only exporting one thing: an instance of b, which has no method1 on it.

Instead, write to properties on the exports object:

module.exports.a = new a();
module.exports.b = new b();

Then:

const x = require('./file.js');

x.a.method1();
// ...

or more typically, with destructuring so you don't need x:

const {a, b} = require('./file.js');

a.method1();
// ...

All of that said: That syntax is the old CommonJS module system. I suggest you learn the newer standard syntax, "ESM" (ECMAScript Modules), added to the JavaScript specification in ES2015:

function A() {
}
A.prototype.method1 = function() { /* ... */ };
A.prototype.method2 = function() { /* ... */ };

function B(){}
B.prototype.method3 = function() { /* ... */ };
B.prototype.method4 = function() { /* ... */ };

export const a = new A();
export const b = new B();

Also note that I've made the constructor functions start with a capital letter, which is the standard convention in JavaScript.

The import would be:

import { a, b } from "./file.js";

a.method1();
// ...

To do that, you add "type": :"module" to your package.json (or use the .mjs file extension, see the linked docs for details). Note though that a large number of npm packages haven't been updated to support ESM yet (not least because supporting both took a while to nail down and is a bit of a pain), so in some cases you have to jump through some (minor) hoops to use them; more here.

(You might also look at the class syntax, which provides a more concise and powerful way to write constructor functions and their associated .prototype objects.)

user_1572470 
module.exports = {
    a,
    b
}

Call it from other file:

const {a, b} = require("./file.js");
user_145046850
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