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There are several promise libraries (the most promising among them seems to be Bluebird, though Q has some popularity as well), which can easily convert callbac

There are several promise libraries (the most promising among them seems to be Bluebird, though Q has some popularity as well), which can easily convert callback-style functions into promises. For example: var b = require('bluebird'), request = b.promisify(require('request')); request(...).then(...) These libraries also have utilities for controlling callback flow -- e.g calling several promises in parallel, which is done in the article with jQuery's $.when, waiting until a certain number finish, etc

iamwil 12y ago
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?
- unspecified 12y ago
  As long as the library follows the "function (err, data)" convention: https://github.com/petkaantonov/bluebird/blob/master/API.md#promisepromisifyfunction-nodefunction--dynamic-receiver---function https://github.com/petkaantonov/bluebird/blob/master/API.md#...
- esailija 12y 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.

iamwil 12y ago

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?

unspecified 12y ago
As long as the library follows the "function (err, data)" convention: https://github.com/petkaantonov/bluebird/blob/master/API.md#promisepromisifyfunction-nodefunction--dynamic-receiver---function https://github.com/petkaantonov/bluebird/blob/master/API.md#...
esailija 12y 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.