Awaiting an event completion in NodeJS before returning

Question

I have a class getter that I want to return a value from only when an event listener has completed. Is there a way to do this?

I am aware that I can wrap it in a Promise and apply it to the chain but it does not follow the modularisation I require the the usage of the application:

class Request{
    get body(){
        console.log('processed before')
        console.log(processed)
        this._request.on('data', chunk => {
                console.log('data received');
                if (null == this._body._text) {
                    this._body._text = "";
                }
                this._body._text += chunk;
            })
            .once('end', () => {
                console.log('processed')
                processed = true;
            });
        console.log('processed after')
        console.log(processed)

        console.log('return this._body')
        return this._body;
    }
}

let req = new Request();
console.log(req.body());

I need the return to only continue and return after the request "end" event has occurred.

Thank-you in advance.

Answer 1

You could generally use async functions here:

async function run(){
 console.log('processed before');
 console.log(processed);

 var processed = await new Promise(function(processed){
 this._request.on('data', chunk => {
        console.log('data received');
        this._body._text = "";
        this._body._text += chunk;
 })
 .once('end', () => {
        console.log('processed')
        processed(true);       
  });
 });

 console.log('processed after');
 console.log(processed);

 console.log('return this._body')
 return this._body;
}

However it is very inefficient to really halt and await execution, thats why it isnt possible in js ( await is just a beautiful .then ), and the async function actually retunrs a promise. So using it as a getter wont work and is a terrible way of doing so. You probably need a non getter approach, or the getter returns the promise:

var obj = {
 get stuff(){
   return run();
 }
};

obj.stuff.then(console.log);
obj.stuff.then(console.log);