CODEWITHSUNDEEP
javascriptrxjsobservable
Grant
Grant

Reputation: 11376

Rx Observable creation / structure

Can anyone explain what the difference is between the following 2 sources? I came across the first block but not sure why it would be preferable to the second.

source 1

Observable
    .of(futureDate)
    .flatMap(date => {
        const delay = date - Date.now();
        return Observable.timer(delay);
    });

source 2

const delay = futureDate - Date.now();
Observable.timer(delay);

Upvotes: 1

Views: 170

Answers (1)

cartant
cartant

Reputation: 58430

The difference becomes apparent when you consider that nothing happens until a subscription is made - and subscriptions could be made sometime after the observables have been created.

When a subscription is made to the first observable, the delay passed to the timer is based upon the current time - that is, the time of subscription.

When a subscription is made the the second, the timer's delay will have been based upon the time at which the observable was created - not upon the time of subscription.

Upvotes: 3

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