Question

45

How can I write a generator in a JavaScript class?

rated 0 times [ 49] [ 4] / answers: 1 / hits: 36171 / 8 Years ago, mon, august 29, 2016, 12:00:00

Usually, I write code like this:

//definition

exports.getReply = function * (msg){

    //...

    return reply; 

}

//usage

var msg = yield getReply ('hello');

but how can I write and use a generator in and out of an es6 class? I tried this:

class Reply{

    *getReply (msg){

        //...

        return reply; 

    }

     *otherFun(){

        this.getReply();  //`this` seem to have no access to `getReply`

    }

}

var Reply = new Reply();

Reply.getReply();   //out of class,how can I get access to `getReply`?

I also tried:

 class Reply{

      getReply(){

         return function*(msg){

            //...

            return reply;

         }

      }

    }

All of these two methods seem to be wrong answers. So how can I write generator functions in a class correctly?

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mireyag

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answered 8 Years ago jananauticat · Accepted Answer

Edit: Add more examples.

Your class definition is (almost) correct.The error was in instantiation var Reply = new Reply();. This tries to redefine variable assigned to class name. Also generator function is expected to yield something. I elaborated a little OP code to show working example.

class Reply {

  //added for test purpose

  constructor(...args) {

      this.args = args;

    }

    * getReply(msg) {

      for (let arg in this.args) {

        let reply = msg + this.args[arg];

        //generator should yield something

        yield reply;

      }

      //next call returns (yields) {done:true,value:undefined}

    }

    * otherFun() {

      yield this.getReply('Nice to meet you '); //yields Generator object

      yield this.getReply('See you '); //Yes, this can access 

      //next call yields {done:true, value:undefined}

    }

    * evenMore() {

      yield* this.getReply('I miss you '); //yields generator result(s)

      yield* this.getReply('I miss you even more ');

    }

}

//now test what we have

const reply = new Reply('Peter', 'James', 'John');

//let and var here are interchangeable because of Global scope

var r = reply.getReply('Hello ');

var msg = r.next(); //{done:false,value:...}

while (!msg.done) {

  console.log(msg.value);

  msg = r.next();

}

var other = reply.otherFun();

var o = other.next(); //{done:false,value:Generator}

while (!o.done) {

  let gen = o.value;

  msg = gen.next();

  while (!msg.done) {

    console.log(msg.value);

    msg = gen.next();

  }

  o = other.next();

}

var more = reply.evenMore();

msg = more.next();

while (!msg.done) {

  console.log(msg.value);

  msg = more.next();

}

//update of 1/12/2019

//more examples

for (let r of reply.getReply('for ')) {

  console.log(r);

}

for (let r of reply.evenMore()) {

  console.log(r);

}

//note that the following doesn't work because of lack of star (*) inside the generator function

for (let r of reply.otherFun()) {

  console.log(r);

}

UPDATE 1/12/2019

As suggested by @BugBuddy for..of loop looks even nicer (But doesn't work in all cases). See updated lines in the snippet.