Utilizing Bluebird Promises
- 1. Unfulfilled (Newborn) Promise Fulfilled (Resolved) Promise Failed (Rejected) PromisePromises Crash Course Nicholas van de Walle
- 2. 13 A resolved promise is essentially a “value”
- 3. A rejected promise is essentially a caught ErrorA rejected promise is essentially a caught Error
- 4. (error only catches OperationalErrors) These errors jump straight to the next “catch” or “error” .catch(fn ( ) { // handlin’ }) .catch(fn ( ) { // handlin’ }); .then(fn ( ) { // executin’ }) .then(fn ( ) { // executin’ }) getUserAsync({ userID: ‘abc’ }) fn(err) { // handlin’ } fn(err) { // handlin’ } fn(err) { // handlin’ }
- 5. Promises allow you to create asynchronous “Pipelines” Sending JSON fn(err) { // handlin’ } Error Handler (Generic) Diff’rent 404’d Puppies Got! … then Get all the user’s puppies 404’d User Got! … then Get me the user
- 6. Creating Promises (A Contrived Example) fn x2Later ( num, callback ) { process.nextTick( fn () { callback( num * 2 ) }) } fn x2Async ( num ) { return new Promise( fn ( resolver, rejector ) { x2Later( num, resolver ) }) }
- 7. Use Promisify (A Contrived Example) fn x2Later ( num, callback ) { process.nextTick( fn () { callback( num * 2 ) }) } x2Async = Promise.promisify( x2Later )
- 8. Just use promisifyAll ( Always do this at the root require ) var fs = Promise.promisifyAll(require(‘fs’)) fs.readFileAsync(file)fs.readFile(file, cb) fs.openAsync(file)fs.open(file, cb) fs.renameAsync(old, new)fs.rename(old, new, cb) fs.mkdirAsync(path)fs.mkdir(path, cb)
- 9. Wrapping non-compliant API’s is easy var getUsersAsync = fn ( userIds ) { return new Promise( fn ( resolve, reject ) { // Noncompliant API uses an object of callbacks getUsers( userIds, { success : fn ( err, data ) { (err) ? reject(err) : resolve(data.users) }, error : fn ( status, obj ) { // TODO (Nicholas): REFACTOR TO BE JSON API COMPLIANT reject( new Promise.OperationalError( status.description ) ) } }) }) }
- 10. Sometimes you need to wait for two (or more) operations to succeeed Sending JSON Do some logic Join’d promises promise Users Got! … spread Join these two GetUser promises
- 11. You can easily manage collections of promises ( Also: settle, any, some, props ) all At least one failed All Successful
- 12. And your functional buddies are here too! ( Also: reduce, each, filter ) map At least one failed All Successful
- 13. Testing Promises is Easy (With Chai as Promised) ( Thanks to Domenic Denicola, now of Google Chrome team ) .should.eventually.equal( ) .should.eventually.equal( ) .should.be.rejectedWith( ) .should.be.rejectedWith( )
- 15. Timers let you control when and if a promise fulfills Timeout Delay … is the opposite of ...
- 16. Bluebird gives you many helpful inspection methods reflect isFulfilled isRejected isPending value reason ? ? ?? ??? ??? Err
- 17. Reflect is a super powerful generic Settle Promise.props({ "First" : doThingAsync().reflect(), "Second” : doFailerAsync().reflect(), "Third" : doSomethingElseAsync().reflect() }).then… No matter what
- 18. Bind lets you share state, w/0 closures Bind to State is passed as ‘this’ Enables Code Reuse
- 19. Resource management is totes easy with Using & Disposer fn getConn() { return pool.getConnAsync() .disposer( fn (conn, promise) { conn.close() }) } using( getConn(), fn(conn) { return conn.queryAsync("…") }).then( fn (rows) { log(rows) }) GC