promise-tap

a small utility for tracing promises

convenience

since this is mostly meant for debugging and quick hackery, require('promise-trace').mix(Promise.prototype) might come in handy for you.

API

promise.tap(onFulfilled, onRejected)

returns a promise that resolves to promise, after promise.then(onFulfilled, onRejected) resolves.

promise.tapDone(onFulfilled, onRejected)

returns promise itself and calls promise.done(onFulfilled, onRejected)

promise.trace(message, timeout)

logs the state transitions of the promise.

example:

Promise.resolve('a').trace('first')
 
Promise.resolve(undefined).then(function() { throw new Error('fail') }).trace('second')
 
new Promise(function(resolve, reject) { setTimeout(function() { resolve('b') }, 500) }).trace('third', 100)

awaiting first #1
awaiting second #1
awaiting third #1
resolved first #1 at Object.<anonymous> (/home/nathan/code/promise-tap/trace.js:5:22): a
failed second #1 at Object.<anonymous> (/home/nathan/code/promise-tap/trace.js:7:73): [Error: fail]
still awaiting third #1 after 100ms
resolved third #1 at Object.<anonymous> (/home/nathan/code/promise-tap/trace.js:9:89): b

wrap(promise)

returns a fresh traceable promise, resolved to the passed one. literally mix(promise.then()).

mix(promise)

makes your promise a traceable one and returns it.