Changes between Initial Version and Version 1 of Ticket #14615


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Timestamp:
Apr 1, 2012, 10:54:49 PM (8 years ago)
Author:
Mark Wubben
Comment:

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  • Ticket #14615 – Description

    initial v1  
    1 For 1.8 I'm looking to introduce a new Deferred API under `dojo/Deferred`, with a backwards compatible wrapper under `dojo/_base/Deferred`.
     1Dojo 1.8 will have a new Deferred API available under `dojo/Deferred`, with a `when()` implementation under `dojo/when`. `dojo.Deferred` will remain `dojo/_base/Deferred`. `dojo/_base/Deferred` also sets `dojo.when`, which *is` the same as `dojo/when`. Instances of `dojo/_base/Deferred` have a `promise` object that is an instance of `dojo/promise/Promise`, i.e. a new promise object.
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    3 Ideally you can use Dojo without ever loading the backwards compatible layer. The most elegant solution is to only include `dojo/_base/Deferred` when `dojo` itself is included. Internal code should never require `dojo` directly and external code can be written in a similar manner.
     3Notable changes:
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    5 `dojo/Deferred` should be the minimal promise API. It'd be good however if we allow a configuration option to swap out its implementation. E.g. `dojo/Deferred` would by default load and return `dojo/promise/Deferred` but this can be changed to `promised-io/promise/Deferred`.
     5* Based on Promises/A, ergo no support for `addCallback`, `callback` etc.
     6* You can `resolve`/`reject`/`progress`/`cancel` a deferred multiple times without errors being thrown, unless a "strict" flag is set.
     7* `resolve`/`reject`/`progress` return the promise.
     8* a reason can be passed to `cancel()` for communicating to the canceler why the deferred needs to be canceled.
     9* `when()` without callbacks always returns a promise.
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    7 Which brings us to the work I'm doing on a Promised-IO rewrite, code for which can be found at <https://github.com/promised-io/core>. This code differs from the CommonJS proposals and the current Dojo implementation in a few ways:
     11Additional changes:
    812
    9 * A reason can be passed to `cancel()` which is then sent to the canceler, allowing for upstream signaling
    10 * `resolve()`, `reject()`, `progress()` and `cancel()` are no-ops on fulfilled promises, unless a second parameter, a `strict` flag, is set to `true`, in which case an error will be thrown
    11 * `resolve()`, `reject()`, `progress()`, `cancel()` and `then()` are bound via closure to the deferred / promise, meaning they can be called without a scope and still work correctly
    12 * Anything is allowed to be an error, even `undefined`, as long as its passed with `reject()` or thrown by a callback
    13 * A custom error class is used for cancel errors
    14 * `promised-io/promise/when` **always** returns a promise and converts foreign promises into "native" promises
    15 
    16 I've also added various sugary methods that do not need to be included in Dojo Core.
    17 
    18 While I intend to copy the logic from my Promised-IO code into Dojo I'm not sure about some of the behavior changes. Especially if we want to make the logic swappable Dojo Core should assume a lowest common denominator.
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    20 To what extend do we need to support older behavior? There are subtle differences between 1.4 and 1.7, which should it meet? What about the error objects when a promise is canceled? What do we do about `dojo/xhr` who's behavior relies on the old deferred logic?
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    22 Similarly, `dojo/DeferredList` is just horrible and should be replaced. Perhaps `dojo/promise/all` analogous to `promised-io/promise/all`.
    23 
    24 Feedback appreciated.
     13* `when()` converts foreign promises.
     14* `isResolved`/`isRejected`/`isCanceled`/`isFulfilled` helpers on deferreds and promises.
     15* `fail`/`both` helpers on promises.
     16* custom `CancelError` subclass of `Error`.
     17* To detect errors (or generally observe the behavior of promises) a tracing mechanism has been added. This replaces logging errors to the console in `dojo/_base/Deferred`.
     18* Introduces `dojo/promise/first` and `dojo/promise/all` as a replacement for `dojo/DeferredList`. The later is unmodified.