Promise's second .then() not failing

google-chrome, javascript, promise

Solution

Why does the second then() has its done handler called instead of the fail one?

Because you handled the error in the first `then()` of the chain already, making the promise resolve with the `"First then: FAIL"` string that you returned from it.

Is this a bug with Chrome?

No, that's how promises are supposed to work.

Do I need to resort to returning pre-resolved/rejected Promises from the .then handlers?

You can do that, yes. Other ways to trigger the second fail handler would be:

Simply omit the first error handler:

prom.then(function(done) {
    console.log("First handler: Done!: Argument: ", done);
    return "First then: DONE";
}).then(function(done) {
    console.info("Second handler: Done!.  Argument: ", done);
}, function(fail) {
    console.error("Second handler: Fail!.  Argument: ", fail);
});

Or rethrow an exception (that's similar to returning a rejected promise):

prom.then(function(done) {
    console.log("First handler: Done!: Argument: ", done);
    return "First then: DONE";
}, function(fail) {
    console.error("First handler: Fail!. Argument: ", fail);
    throw new Error("First then: FAIL"); // or: throw fail;
    // alternatively, you can return a rejected promise:
    return Promise.reject(new Error("First then: FAIL"));
}).then(function(done) {
    console.info("Second handler: Done!.  Argument: ", done);
}, function(fail) {
    console.error("Second handler: Fail!.  Argument: ", fail);
});

Problem

Original source

Related problems

• Chained promises not passing on rejection
• Chained promises not passing on rejection