Readable implementation in typescript :

Question

I implemented the Readable stream in Typescript. Here's how :

import * as stream from 'stream';

export class Readable extends stream.Readable {

    lastLineData = '';
    objectMode = true;
    ended = false

    constructor() {
        super({objectMode:true});
    }

    _read = () => {}

    send = data => {
        if (!this.ended) {
            this.push(data)
        }
    }

    errorAndCancel = err => {
        if (!this.ended) {
            this.emit('error', err)
            this.push(null)
            this.ended = true
        }
    }

    end = () => {
        if (!this.ended) {
            this.push(null)
            this.ended = true
        }
    }
}

On some machine (Gitlab CI with electronuserland/wine-02.18) or Windows Server machine with node.js v10 give me this error :

[08:11:38]  typescript: C:/git/celliers/synchro-pos/src/providers/xmlStreamParser/Readable.ts,

        Class 'Readable' defines instance member function '_read', but extended class 'Readable' defines it as
        instance member property.

  L13:      _read = () => {}

If I change _read to read, it doesn't work neither (same message). I question my implementation is not right. Is anyone able to tell me what I'm doing wrong?

Thanks!

Collierre · Accepted Answer · 2019-08-29 20:46:06Z

1

In Typescript v.3 this would not be a problem. However you must be using an older version, where what you are trying to do is not allowed.

The error says that your class is defining _read as a property, whereas the parent class defines it as a function. Therefore your child class is incorrectly extending its parent. You need to either upgrade to Typescript 3, or to change your property:

_read = () => {}

To a method:

_read() {}

answered Aug 29, 2019 at 20:46

Collierre

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1 Comment

Mathieu G Over a year ago

I used your suggestion instead of upgrading to Typescript 3. Thanks it works!

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