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0 pointsiamwil11y ago0 comments

I hadn't heard of bluebird at all. Does it work for any library you require?

When I used promises for real in a section of my code processing data:

1) I found it hard to use mostly because of all the work I had to do to "lift" non promise code up into promises, before I could use them.

2) When chaining them, it wasn't clear how you would handle a "fan-out", where a piece of data generated an array, which you then had to process with callbacks.

3) Unless I inserted a fail() after every then(), it was hard to tell where exactly in the chain something failed, and the stack trace wasn't very helpful.

I suspect maybe I'm doing something wrong--that even though you can chain promises sequentially, you generally want to make functions using promises, that you can then chain? I still haven't seen well written promise code. Anyone got examples other than toy examples?

0 comments

esailija11y ago

It does work for any library that uses callbacks - a node library that uses callbacks but not the node js callback convention has a bug.

1) There is not much work in promisifying libraries, for example the entire redis library can be promisified using 2 lines:

    var Promise = require("bluebird");
    var redis = require("redis");
    Promise.promisifyAll(redis.RedisClient.prototype);
    Promise.promisifyAll(redis.Multi.prototype);

After those lines all redis client objects have promise-returning versions of the methods. E.g. `redisClient.getAsync()` is the promise-returning version of `redisClient.get()`

2) Mixing callbacks and promises will result in very ugly code, see 1) to avoid it.

3) Forget about .fail(), this is not how promise error handling works. Use `.catch()` like you would use try catch. In your case that means not using it at all - then a full stack trace is automatically logged. Try catch is meant to be used with expected errors like file not existing, not bugs.

unspecified11y ago

As long as the library follows the "function (err, data)" convention:

https://github.com/petkaantonov/bluebird/blob/master/API.md#...

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