How do I implement recursive promises?

Question

I have written a retry mechanism that should return a promise:

private connect(): Promise<any> {
      return new Promise((resolve, reject) => {
          if(this.count < 4) {
             console.log("count < 4, count:"+this.count);
             this.count++;
             return this.connect();
            } else {
              resolve("YES");
            }
        });
    }

If I call:

t.connect().then((data:any)=>{ console.log("YES:"+data)});

I would like once count >= 4 and resolve is called to be able to trigger the above "then".

Answer 1

You need to resolve inner promise with the new one, return this.connect() is not enough:

function connect(): Promise<any> {
  return new Promise((resolve, reject) => {
    if (this.count < 4) {
      console.log("count < 4, count:" + this.count);
      this.count++;
      resolve(this.connect());
    } else {
      resolve("YES");
    }
  });
}

Note, how you resolve with new recursive promise with resolve(this.connect());.

Check the demo below.

function connect() {
  return new Promise((resolve, reject) => {
    if (this.count < 4) {
      console.log("count < 4, count:" + this.count);
      this.count++;
      resolve(this.connect());
    } else {
      resolve("YES");
    }
  });
}

const t = {count: 0, connect}

t.connect().then(data => console.log(`YES: ${data}`));