Is there a issue by promise-chaining?

[deleonio]

Hello,

I try to chain promises correct. But there is something magic.

fdescribe('Test then by promise-chaining', function () {

  function httpPromise(counter, length) {
    return new Promise(function (resolve, reject) {
      if (counter >= length) {
        resolve(counter);
      } else {
        reject(counter += 1);
      }
    });
  }

  function thenFirst() {
    return new Promise(function (resolve) {
      var length = 2;
      httpPromise(0, length)
        .then(function (counter) {
          resolve(counter);
        })
        .catch(function (counter) {
          console.log('1', counter);
          return httpPromise(counter, length)
            .catch(function (counter) {
              console.log('2', counter);
              return httpPromise(counter, length)
                .catch(function (counter) {
                  console.log('3', counter);
                  return httpPromise(counter, length);
                });
            });
        });
    });
  }

  function thenLast() {
    return new Promise(function (resolve) {
      var length = 2;
      httpPromise(0, length)
        .catch(function (counter) {
          console.log('1', counter);
          return httpPromise(counter, length)
            .catch(function (counter) {
              console.log('2', counter);
              return httpPromise(counter, length)
                .catch(function (counter) {
                  console.log('3', counter);
                  return httpPromise(counter, length);
                });
            });
        })
        .then(function (counter) {
          resolve(counter);
        });
    });
  }

  it('then first (failed)', function (done) {
    thenFirst()
      .then(function (result) {
        console.log(result);
        done();
      });
  });

  it('then last (completed)', function (done) {
    thenLast()
      .then(function (result) {
        console.log(result);
        done();
      });
  });

});

Error: Timeout - Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL.

[taylorhakes]

@martinoppitz I am having a little trouble following your test. What is the expected behavior for each test?

[deleonio]

If the then comes first, the test failed. Why?

[taylorhakes]

Promise chains execute from top to bottom. Once a part of the chain is skipped, it doesn't go back. In your first example, the first httpPromise gets rejected, so the first then is skipped (because rejected is an error) and it goes to the first catch (after the then). Eventually the catch returns a resolved Promise, but the firstthen has already been skipped. It looks for another then, but there isn't one. The Promise never gets resolved because the call resolve was in the first then (that was skipped).

I may be missing something, but does that make sense? Does the first test pass with some other library? I tried with native Promise and it fails there too.

[deleonio]

Thanks for the explanation. I think I now understand it. 👍