javascript ES6 class/method scope

Question

I can't figure out how to correct the context of my methods.

I have this class:

export default class Handler {

    constructor() {
        // init
    }

    handleMessage(channel, user, message) {
        this.handleDefault(channel, user, message);
    }

    handleDefault(chanenl, user, message) {
        // do stuff
    }
}

it is called by this method and class

export default class Bot {

    constructor() {
        this.irc     = irc // has an event emitter irc.event
        this.handler = new Handler();
        this.readIRC();
    }

    readIRC() {
        this.irc.event.on('message', this.handler.handleMessage);
    }
}

The problem is in the first class inside handleMessage is this not the class anymore but the eventEmitter so I can't call my handleDefault method.

How do I work with contexts corretly in ES6 ?

You seem to be asking about the **`this` context**, not the *scope*. — Bergi, Mar 23 '16 at 16:06

thefourtheye · Answer 1 · 2016-03-23T16:16:05.347

4

You just have to bind handleMessage to this.handler, either with

Function.prototype.bind

this.irc.event.on('message', this.handler.handleMessage.bind(this.handler));

or with an Arrow function,

this.irc.event.on('message', () => this.handler.handleMessage());

In both these cases, when the handleMessage function is invoked on message event, the this within handleMessage will refer the this.handle object.

If you like to pass arguments to the event handler, you can define the arrow function like this

this.irc.event.on('message', (err, msg) => this.handler.handleMessage(err, msg));

edited Mar 23 '16 at 16:16

answered Mar 23 '16 at 16:03

thefourtheye

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If I use an Arrow function how do I pass arguments correctly. – gempir Mar 23 '16 at 16:10
@danielps1: The same way you do it in `handleMessage` itself: define the parameters and pass them along. Or use rest parameter and spread argument. – Felix Kling Mar 23 '16 at 16:12
oh yeah. I actually had it correct just had a stupid typo. thank you! – gempir Mar 23 '16 at 16:15
@danielps1 Exactly like Felix explained. I just included a simple example. PTAL. – thefourtheye Mar 23 '16 at 16:16

javascript ES6 class/method scope

1 Answers1