ES6 classes, with parent in different file, and node.js?

Question

What is the right way to use a class defined in one file and extend it another, in node.js?

Currently I have:

'use strict'

class BasePageHandler {

    constructor(app, settings, context) {

    }
}

return module.exports;

In the 'child' class file I have:

'use strict'

var BasePageHandler = require ('./../BasePageHandler.js');

class FrontpagePageHandler extends BasePageHandler {
    constructor(app, settings, context) {
         super(app, settings, context);
         this.settings = settings;
         this.context = context;
    }
}

This fails with the following error:

TypeError: Class extends value #<Object> is not a function or null

Note, if I have the BasePageHandler in the same file then it works, so it is really when the class is in another file I have an issue.

Currently using node 4.4.0.

You may want to use ES6 native modules with the Common JS transform plugin for Babel, instead module.exports. That way, your code will stay future-ready for when Node implements modules natively. — Dan Dascalescu
– Dan Dascalescu, Commented Oct 3, 2016 at 1:51

madox2 · Accepted Answer · 2016-03-30 21:17:32Z

39

You need to correctly export your class inBasePageHandler.js file:

module.exports = BasePageHandler;

answered Mar 30, 2016 at 21:17

madox2

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5 Comments

Andre M Over a year ago

Indeed. I missed the obvious :)

CodingWithSpike Over a year ago

I'm pretty sure you can also just put it on 1 line: module.exports = class BasePageHandler { that way if you rename the class, it's 1 less place to change it later.

James111 Over a year ago

Event after doing this, I'm still having the same issue? I'm using the harmony_destructuring flag!

user3817050 Over a year ago

I had an issue similar where I was trying to return the class by making module.exports into a function. It worked but not as expected. By simply defining module.exports to be the class, everything worked as expected.

Md Alamin Over a year ago

I did it too, but it does not work for me, any other solution please @madox2

Noam Manos · Accepted Answer · 2017-03-17 19:35:24Z

17

The accepted answer is technically fine, but really if you're using ES6 then you should go all in and use ES6 export/import.

/*jshint esversion: 6 */

class BasePageHandler {
    constructor(app, settings, context) {
    }
}

export default BasePageHandler;

and then:

/*jshint esversion: 6 */

import BasePageHandler from './../BasePageHandler.js';

class FrontpagePageHandler extends BasePageHandler {
    constructor(app, settings, context) {
         super(app, settings, context);
         this.settings = settings;
         this.context = context;
    }
}

edited Mar 17, 2017 at 19:35

Noam Manos

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answered Mar 10, 2017 at 3:26

jonlink

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2 Comments

Noam Manos Over a year ago

BTW, there's no need 'use strict' in ES6 - it's enforced by default.

Kudapucat Over a year ago

When I do this I get "SyntaxError: Cannot use import statement outside a module" And I cannot for the life of my figure out why. What am I missing?

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