尝试在类内调用emit方法时，从EventEmitter扩展的类上的未定义“ this”

Question

I'm trying to use a custom event emitter to handle a webhook, but when calling a method from my class I always get 'this' as undefined

serviceWebhook.js

class WebhookHandler extends EventEmitter{
  constructor (){
    super();
  }
  receiver(req, res){
    try {
      res.sendStatus(200);
      if (req.body && req.body.action) {
        this.emit(req.body.action, req.body)
      }
    } catch (error) {
      console.log(error)
    }
  }
}
module.exports = {
  WebhookHandler: WebhookHandler
}

index.js

var webhookh = new serviceWebhook.WebhookHandler();
router.post('/webhookendpoint', webhookh.receiver);
webhookh.on('action_one', function name(message) {
  console.log('EMITTED')
  console.log(message)
}

This is the error I get:

TypeError: Cannot read property 'emit' of undefined

I have also tried this:

super.emit(req.body.action, req.body)

But then I get this error:

TypeError: Cannot read property '_events' of undefined

Answer 1

Passing the receiver method of an instance of your WebhookHandler class to the callback of your router moves the lexical scope of the method. Try: router.post('/webhookendpoint', webhookh.receiver.bind(webhookh)); This will bind the scope of this within the callback to that of your instance of WebhookHandler.