CODEWITHSUNDEEP
javascriptpromisebluebird
Ilia Sidorenko
Ilia Sidorenko

Reputation: 2715

Perform an intermediate action and carry over the previous result in bluebird

Is there a shorthand which would allow to get the value of the Promise and push it forward the promise chain without explicitly returning it?

In other words, is there a shorthand syntax for the following in bluebird:

.then(result => { callSomething(result); return result })

Upvotes: 0

Views: 46

Answers (2)

Jaromanda X
Jaromanda X

Reputation: 1

If your going to use this pattern often, why not make a generic method for it

Promise.prototype.skip = function skip(fn, onRejected) {
    return this.then(value => Promise.resolve(fn(value)).then(() => value), onRejected);
};

Let's say your example callSomething returns a promise

function callSomething(v) {
    console.log('skip got', v);
    // this promise will be waited for, but the value will be ignored
    return new Promise(resolve => setTimeout(resolve, 2000, 'wilma'));
}

now, b using skip, instead of then, the incoming fulfilled value, in this case fred, will just pass on the following then, but AFTER the promise returned by callSomething is fulfilled

Promise.resolve('fred').skip(callSomething).then(console.log); // outputs "fred"

However, it doesn't matter if callsomething doesn't return a Promise

Upvotes: 1

Andrea
Andrea

Reputation: 3440

You can use the Comma operator inside your arrow function's body (without curly braces):

.then(result => (callSomething(result), result)

The comma operator

evaluates each of its operands (from left to right) and returns the value of the last operand.

So, result is returned by expression:

(callSomething(result), result)

Then, the arrow function without curly braces, returns the value of the expression specified as its body. For this reason, result is returned.

Upvotes: 1

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