orElse

Transforms a failed future into a new future.

This feature is experimental!

This API is still experimental, so it may change or be removed in future versions. You should not rely on it for production applications.

Signature

value(handler)

Type(what is this?)

(Future 'f 's).(('f) => Future 'f2 's2) => Future 'f2 's

Documentation

Transforms a failed future into a new future.

Example:

const { rejected, of } = require('folktale/concurrency/future');

of(1).orElse(x => of(x + 1)).listen({
  onResolved: (value) => $ASSERT(value == 1)
});

rejected(1).orElse(x => of(x + 1)).listen({
  onResolved: (value) => $ASSERT(value == 2)
});

rejected(1).orElse(x => rejected(x + 1)).listen({
  onRejected: (value) => $ASSERT(value == 2)
});

Properties

Source Code

Defined in source/concurrency/future/_future.js at line 24, column 0

orElse(handler) {
    let deferred = new Deferred();      // eslint-disable-line prefer-const
    this.listen({
      onCancelled: ()     => deferred.cancel(),
      onResolved:  value  => deferred.resolve(value),
      onRejected:  reason => {
        handler(reason).listen({
          onCancelled: ()        => deferred.cancel(),
          onResolved:  value     => deferred.resolve(value),
          onRejected:  newReason => deferred.reject(newReason)
        });
      }
    });

    return deferred.future();
  }