Straightforward Way to Extend Class in Node.js

Question

I am moving a plain Javascript class into Node.js. In the plain Javascript I use:

class BlockMosaicStreamer extends MosaicStreamer{
}

I can't seem to find a simple way to implement this in Node.js. In my node project in BlockMosaicStreamer.js I have:

'use strict'; 
function BlockMosaicStreamer(){
}

How would I extend MosaicStreamer which is in ./MosaicStreamer.js?

'use strict'; 
function MosaicStreamer(){
}

[`util.inherits`](https://nodejs.org/api/util.html#util_util_inherits_constructor_superconstructor) — Bergi, Apr 19 '16 at 18:34
@Bergi Can you elaborate a bit? I would need to add `util`, then would get the desired functionality with `util.inherits(BlockMosaicStreamer, MosaicStreamer)`? — Sara Fuerst, Apr 19 '16 at 18:57
Yes, and put a `MosaicStreamer.call(this, …)` "super" call in the `BlockMosaicStreamer` constructor. — Bergi, Apr 19 '16 at 19:27
@Bergi I'm not familiar with how the "super" call would work. What would be replaced by the ...? — Sara Fuerst, Apr 19 '16 at 19:40
Any arguments that you want to pass into the parent constructor (possibly none). It's just [`call`ing](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call) the constructor on the new instance to get it initialised - no magic. — Bergi, Apr 19 '16 at 19:45

score 24 · Accepted Answer · answered Apr 19 '16 at 18:29

24

It depends how you defined your first class, I suggest using something like this:

class SomeClass {
}

module.exports = SomeClass

then in your extend:

const SomeClass = require('./dir/file.js')

class MyNewClass extends SomeClass {
}

module.exports = MyNewClass

answered Apr 19 '16 at 18:29

Nick Messing

However, my classes are defined as shown in the question. Using `class` in node causes a lot of issues – Sara Fuerst Apr 19 '16 at 18:31
@tibsar: Then use a transpiler. There should be nothing that stops you from using ES6 today. – Bergi Apr 19 '16 at 18:34
@tibsar, you can update node.js, I'm using 5.9.1 and it works just fine. – Nick Messing Apr 19 '16 at 18:41
Is there absolutely no way to do it the way I'm doing it? – Sara Fuerst Apr 19 '16 at 18:54
@tibsar, it will take way more time then writing in es6 and transpiling or updating node – Nick Messing Apr 19 '16 at 18:57
@NickMessing Can you show me how you would do it this way? – Sara Fuerst Apr 19 '16 at 18:57
@tibsar, take a look at https://www.typescriptlang.org/play/ choose Classes Example and take a look at JavaScript result. – Nick Messing Apr 21 '16 at 12:04

1 Answers1