Introduction

TS-Promise is a fast, robust, type-safe promise library.

Features:

• Promises/A+ 1.1 compliant
• ES6 Promise interface compatible
• Long stack traces support (switchable at runtime!)
• Fast
• Efficiently supports infinite recursion (with and without long stack traces)
• Early throwing of unhandled rejections with .done()
• No progression handlers
• Optional explicit promise chain flushing, useful for test frameworks
• Readable code (not too many tricks)

For other planned features, see the TODO below.

Usage example

Install using npm:

cd your-project
npm install --save ts-promise

If you use TypeScript, use "moduleResolution": "node" in your tsconfig.json to let it automatically pick up the typings of this package.

// Example using ES6 syntax (e.g. using Typescript or Babel)

import Promise from "ts-promise";
// or e.g. var Promise = require("ts-promise").Promise;

// Hello world
Promise.resolve("hello world").then((v) => {
	console.log(v);
});

// Long stack traces demo
Promise.setLongTraces(true);
var p = Promise.resolve();
p.then(() => {
	return Promise.reject(new Error("my error"));
}).catch((e) => {
	console.error(e.stack);
});

Example output of the above:

"hello world"
Error: my error
    at /home/martin/src/promise-example/example.js:9:35
    at Promise._unwrap (/home/martin/src/ts-promise/src/lib/Promise.ts:542:20)
    at Promise._unwrapper (/home/martin/src/ts-promise/src/lib/Promise.ts:557:19)
    at CallQueue.flush (/home/martin/src/ts-promise/src/lib/async.ts:47:4)
    at Async.flush (/home/martin/src/ts-promise/src/lib/async.ts:116:19)
    at Async._scheduledFlush (/home/martin/src/ts-promise/src/lib/async.ts:95:9)
    at Object.Async._flusher [as _onImmediate] (/home/martin/src/ts-promise/src/lib/async.ts:58:50)
    at processImmediate [as _immediateCallback] (timers.js:330:15)
  from Promise at:
    at Function.Promise.reject (/home/martin/src/ts-promise/src/lib/Promise.ts:211:11)
    at /home/martin/src/promise-example/example.js:9:28
    at Promise._unwrap (/home/martin/src/ts-promise/src/lib/Promise.ts:542:20)
    at Promise._unwrapper (/home/martin/src/ts-promise/src/lib/Promise.ts:557:19)
    at CallQueue.flush (/home/martin/src/ts-promise/src/lib/async.ts:47:4)
    at Async.flush (/home/martin/src/ts-promise/src/lib/async.ts:116:19)
    at Async._scheduledFlush (/home/martin/src/ts-promise/src/lib/async.ts:95:9)
    at Object.Async._flusher [as _onImmediate] (/home/martin/src/ts-promise/src/lib/async.ts:58:50)
    at processImmediate [as _immediateCallback] (timers.js:330:15)
  from previous:
    at Promise.then (/home/martin/src/ts-promise/src/lib/Promise.ts:181:15)
    at Object.<anonymous> (/home/martin/src/promise-example/example.js:8:3)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:902:3
  from previous:
    at Function.Promise.resolve (/home/martin/src/ts-promise/src/lib/Promise.ts:205:11)
    at Object.<anonymous> (/home/martin/src/promise-example/example.js:7:25)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:902:3

Docs

All public methods and interfaces have JSDoc comments, so if your favorite IDE supports these, you'll have instant inline documentation.

That said, the library's interface should be very unsurprising: basically ES6 Promises with some extras.

For your convenience, here's a list of what's available on Promise.

Static methods on Promise:

• constructor(resolver: (resolve: (value: T | Thenable<T>) => void, reject: (reason: Error) => void) => void) Create a new Promise by passing a function that accepts resolve and reject functions. Example:

  var p = new Promise((resolve, reject) => {
      setTimeout(() => {
          resolve(42);
          // or e.g.: reject(new Error("boom"));
      }, 100);
  });

  See ES6 Promise spec for details.
• static resolve<R>(value: R | Thenable<R>): Promise<R> Create an immediately resolved promise (in case of a 'normal' value), or a promise that 'follows' another Thenable (e.g. a Promise from another library). See ES6 Promise spec for details.
• static resolve(): Promise<void> Convenience alias to create a void-Promise (for type-safety). See ES6 Promise spec for details.
• static reject(reason: Error): Promise<any> Create an immediately rejected promise with reason as its rejection value. See ES6 Promise spec for details.
• static all<X>(thenables: (X | Thenable<X>)[]): Promise<X[]> Create a promise that resolves to an array containing the results of resolving all Thenables ('promises') in the input array (or simply their value, if they're not a Thenable). If any of the input promises leads to a rejection, the output promise is rejected with the reason of the first rejected promise. See ES6 Promise spec for details.
• static race<X>(thenables: (X|Thenable<X>)[]): Promise<X> Create a promise that is resolved or rejected with the first resolved or rejected Thenable (or 'plain' value) in the array. Note: the promise will never resolve if the input array is empty.
• static delay(ms: number): Promise<void> Create a promise that resolves with undefined after ms milliseconds.
• static delay<R>(value: R|Thenable<R>, ms: number): Promise<R> Create a promise that resolves with given value after ms milliseconds. If value is a Thenable, the timer will start when it is resolved. If value is rejected, the resulting promise is also rejected, without waiting for the timer.
• static defer<X>(): Deferred<X> Return an object containing a promise and its corresponding resolve and reject functions. Note: most users will typically want to use the Promise constructor instead, as e.g. thrown errors will then automatically lead to a rejected promise.
• static setLongTraces(enable: boolean): void Enable or disable long stack trace support. See Example in README. Can be enabled and disabled at runtime, and 'traced' and 'untraced' promises can be mixed freely. Disabled by default, as it does incur both a performance and memory overhead (though still about twice as fast as Q without long traces...).
• static flush(): void Recursively flush the async callback queue until all .then() and .done() callbacks for fulfilled and rejected Promises have been called. May throw an error (e.g. UnhandledRejectionError). It is safe to call flush() again afterwards. It is an error to call flush while it is already running. Useful in e.g. unit tests to advance program state to the next 'async tick'.
• static setTracer(tracer: (promise: Promise<any>, msg: string) => void): void Debug helper to trace promise creation, callback attaching, fullfilments, etc. Call with null to disable (default), or pass a function that's called during various stages in a Promise's lifecycle. Note: this function's API is likely going to change in the future (and may even be removed completely.)

Methods on Promise instances:

• then<R>(onFulfilled?: (value: T) => R | Thenable<R>, onRejected?: (reason: Error) => R | Thenable<R>): Promise<R> See ES6 Promise spec
• catch<R>(onRejected?: (reason: Error) => R | Thenable<R>): Promise<R> See ES6 Promise spec
• done<R>(onFulfilled?: (value: T) => void | Thenable<void>, onRejected?: (reason: Error) => void | Thenable<void>): void done() behaves like .then() but does not return a new promise. Instead, it throws an UnhandledRejectionError when the final result of the promise chain is a rejected Promise (.reason property of the error). Note that it is technically safe to 'continue' the program after e.g. catching the error through Node's uncaughtException, or when running in a browser.
• finally(handler: (result: Promise<T>) => void|Thenable<void>): Promise<T> Asynchronous equivalent of try { } finally { }. Runs handler when promise resolves (fulfilled or rejected). Handler is passed the current promise (which is guaranteed to be resolved), and can be interrogated with e.g. isFulfilled(), .value(), etc. When handler returns undefined or its promise is fulfilled, the promise from finally() is resolved to the original promise's resolved value or rejection reason. If handler throws an error or returns a rejection, the result of finally() will be rejected with that error. Example: someLenghtyOperation().finally((result) => { if (result.isFulfilled()) { console.log("succeeded"); } else { console.log("failed", result.reason()); } });
• isFulfilled(): boolean Returns true when promise is fulfilled, false otherwise.
• isRejected(): boolean Returns true when promise is rejected, false otherwise.
• isPending(): boolean Returns true when promise is still pending, false otherwise.
• value(): T Returns fulfillment value if fulfilled, otherwise throws an error.
• reason(): any Returns rejection reason if rejected, otherwise throws an error.
• toString(): string Returns a human-readable representation of the promise and its status.
• inspect(): string Returns a human-readable representation of the promise and its status.
• delay(ms: number): Promise<T> Create a promise that resolves with the same value of this promise, after ms milliseconds. The timer will start when the current promise is resolved. If the current promise is rejected, the resulting promise is also rejected, without waiting for the timer.

TODO

Planned features (in fairly arbitrary order):

• Auto-generate online docs using TypeDoc
• Replace/update the (slightly out-of-date) docs above
• Implement property-based catch() predicate (error constructor(s) and function already done)
• Possibly-unhandled-rejection detection
• Non-V8-support: it works in non-V8, but long stack traces aren't available
• Switch (back) to process.nextTick() / MutationObserver etc
• Implement .promisify()
• Simplify code somewhat more (most notably reduce duplication of 'called'-logic when resolving, maybe also slightly simplify async callback queue implementation)

Interesting ideas that need further investigation:

• Support for differentiating between programmer errors (e.g. assertions, null derefences) and 'expected' errors. E.g. bluebird has .error() and the concept of OperationalError, but this may not be the best way to interoperate with other libraries.

• Possibly-unterminated-promise-chain detection. Wild idea that could help to always make sure to either return a promise from a function, or properly terminate it, thus reducing the chance of a PossiblyUnhandledRejectionError at runtime.

• .settle() and/or other form of simply waiting for a bunch of void-promises, but await all of them before returning, even in case of errors. To prevent e.g. shutting things down while some tasks were still running.

• Split off async callback queue and stack trace handling into separate packages to allow re-use by other packages.

• UMD support? Submit an issue if you think this is useful to you, as I'm more of a browserify guy myself.

Development

Found an issue? Have an idea? Wanna help? Submit an issue!

git clone https://github.com/poelstra/ts-promise
cd ts-promise
npm install
# hack hack, code code...
npm run prepublish

Changelog

0.3.0 (2016-02-26):

• Switch to "moduleResolution": "node"-compatible typings -- To use these typings, simply put that setting in your tsconfig.json and remove the (manual) reference to the ts-promise.d.ts file from your project.
• Update to latest Typescript (1.8.2)
• Update to latest TSLint, fix linting errors
• async.setScheduler() now uses undefined (instead of null) to reset, but the old behaviour still works (though deprecated)

0.2.5 (2016-02-08):

• Replace previous setImmediate hack with non-global-polluting one (#8)

0.2.4 (2016-01-30):

• Stub setImmediate in case of browserify'ed environment (#8)

0.2.3 (2015-08-27):

• Fix stack overflow for very long unresolved promise chains
• Simplify and document internal unwrapping logic

0.2.2 (2015-08-04):

• Implement .finally() (#3)
• Add Inspection<T> interface (#4)
• Don't confuse users by showing our internal stack trace when Node didn't provide one for UnhandledRejectionError

0.2.1 (2015-06-24):

• Improve stack trace for UnhandledRejectionError
• Allow specifying Error classes with different constructor arguments in .catch()

0.2.0 (2015-06-23):

• Allow passing predicate to .catch() (Error class or array of them, or a custom matching function)
• Add .return() and .throw() helpers
• Document all public members of Promise and UnhandledRejectionError
• Stricter typing for Promise.reject(), no longer returns Promise<any> by default
• Require .then() and .catch() to have first callback (for typing only, implementation supports full Promises/A+)
• Include .ts sources to not confuse debugger due to sourcemaps also being included
• Fix building on Windows

0.1.5 (2015-05-17):

• Add Promise.race()
• Add .delay() on Promise and instance

0.1.4 (2015-05-13):

• Add longStackTraces support to .done()
• Export VoidDeferred interface and allow resolving it with a Thenable
• Add .toString() and .inspect()

0.1.3 (2015-05-09):

• Add Promise.defer()
• Add stack to BaseError
• Add rejection reason to UnhandledRejectionError
• 100% code coverage

0.1.2 (2015-05-07):

• Fix bundled .d.ts file for default export
• Add synchronous inspection API
• Export BaseError (to be moved to separate package later)

0.1.1 (2015-05-06):

• Transparent support for mocked timers (e.g. Sinon.useFakeTimers())

0.1.0 (2015-05-04):

• Initial version

License

The MIT license.