如何从Promise内部将函数作为预订返回

Question

I've been returning requests from my functions like this:

makeConnection(data: any) {
    console.log('makeConnection');
    return this.api.get(data.url, data.dataToSend);
  }

So I can subscribe like this: makeConnection.subscribe();

Now I need to check if a variable named urls is set before making an API call So I thought of making a promised function like this

checkIfUrlsPresent():Promise<boolean> {
    return new Promise((resolve, reject) => {
      if(this.urls) {
        resolve(true);
        return;
      }
      this.api.get('/service', null).subscribe((response) => {
        console.log(response);
        this.urls = response.value.urls;
        resolve(true);        
      });
    });
  }

And now my service functions look like this:

requestService(data) {
 this.checkIfUrlsPresent().then(() => {
      console.log('requestService');
      let dataToSend = this.api.createFormData(data);
      return this.api.post('/service/request/', dataToSend);
    })    
}

But now I won't be able to subscribe to my function like requestService(data).subscribe() So my question is how to keep my present flow working while adding this promise or is there any way to check that my variable is set before making a call while keeping this flow working.

Note: The problem is that I'm making all my api calls from one files and there are too many functions that calls these APIs so I need this way so that I won't need to make changes in all my pages to check if url is present.

Answer 1

Almost there. need to return the promise inside the function as well

requestService(data) {
    return this.checkIfUrlsPresent().then(() => { // return the promise
      console.log('requestService');
      let dataToSend = this.api.createFormData(data);
      return this.api.post('/service/request/', dataToSend);
    })    
}

Answer 2

Have requestService return the chained promises, and call .then on it:

requestService(data) {
  return this.checkIfUrlsPresent().then(() => {
    console.log('requestService');
    let dataToSend = this.api.createFormData(data);
    return this.api.post('/service/request/', dataToSend);
  })
}

// ..

instance.requestService(someData)
  .then(service => service.subscribe())