CODEWITHSUNDEEP
javascriptasynchronouspromiserxjs
user2355104
user2355104

Reputation: 82

(Javascript) How to return two promises in one function on different condition

I have a function calc(), which may have following:

calc() {
    ...
    if (condition) {
        return new Promise(...) ; // promise1
    }
    else {
        return new Promise(...); // promise2
    }
}

The function calls it will act on these two promises differently:

calc().then()=>{ do something; } // if promise 1;
      .then()=>{ do nothing; } // if promise 2;

Is it possible to do?

The reason I am asking is that calc() itself is an asynchronous function. It is subscribing to some process like:

calc () {

    subscribe(()=> { do something and need to flash upper caller that is done;}
}

so if calc() does not receive signal from another process, it will not yield results, and upper caller does have the necessary data to proceed.

Upvotes: 1

Views: 91

Answers (1)

Ahmed Saeed
Ahmed Saeed

Reputation: 92

Assuming you know the result of the condition synchronously. Why not wrap the promises in an object and have a property such as id, to denote which promise was returned?

calc() {
    ...
    if (condition) {
        return { id: 1, promise: new Promise(...) }; // promise1
    }
    else {
        return { id: 2, promise: new Promise(...) }; // promise2
    }
}

You can then decide what to do with the promises based on the id returned.

const result = calc();

if(result.id === 1){
    result.then()=>{ do something; } // if promise 1;
}
else if(result.id === 2) {
    result.then()=>{ do nothing; } // if promise 2;
}

Upvotes: 1

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