JavaScript Promises - Thinking Sync in an Async World

Transcript

1. JavaScript Promises Thinking Sync in an Async World then

2. Kerrick Long Things I make and do Where to find

   me online twitter.com/KerrickLong github.com/Kerrick Lead Front-end Developer! at Second Street KerrickLong.com www. meetup.com/STLEmber

3. try {! console.log(getLatestGrade(getStudent(name)));! }! catch (error) {! logError(error);! }! finally

   {! logOut();! }!

4. try {! console.log(getLatestGrade(getStudent(name)));! }! catch (error) {! logError(error);! }! finally

   {! logOut();! }! XMLHttpRequest

5. getStudent(name, function(student) {! getLatestGrade(student, function(grade) {! console.log(grade);! logOut();! });! });!

6. var handleError = function(error) {! logError(error);! logOut();! };! getStudent(name, function(error,

   student) {! if (error) return handleError(error);! getLatestGrade(student, function(error, grade) {! if (error) return handleError(error);! console.log(grade);! logOut();! });! });!

7. var handleError = function(error) {! logError(error);! logOut();! };! getStudent(name, {!

   error: handleError,! success: function(student) {! getLatestGrade(student, {! error: handleError! success: function(grade) {! console.log(grade);! logOut();! },! })! },! });!

8. try {! console.log(getLatestGrade(getStudent(name)));! }! catch (error) {! logError(error);! }! finally

   {! logOut();! }! Awesome

9. var handleError = function(error) {! logError(error);! logOut();! };! getStudent(name, {!

   error: handleError,! success: function(student) {! getLatestGrade(student, {! error: handleError! success: function(grade) {! console.log(grade);! logOut();! },! })! },! });! Awkward.

10. getStudent(name)! .then(getLatestGrade)! .then(console.log)! .catch(logError)! .then(logOut)! ;! Promises

11. None

12. Promise Basics

13. Promise Basics Consuming Promises

14. Promise Basics Consuming Promises Creating Promises

15. Promise Basics Consuming Promises Creating Promises Advanced Techniques

16. Promise Basics

17. Getting Promises

18. None

19. RSVP.js Q.js • Bluebird

20. RSVP.js Q.js • Bluebird Promises/A+

21. Promise Guarantees

22. Always Async

23. Always Async Returns a Promise

24. Always Async Returns a Promise Handled Once

25. Always Async Returns a Promise Handled Once Then’able

26. Promise States

27. Promise States Pending Fulfilled Rejected

28. Promise States Pending Fulfilled Rejected } Settled

29. Promise States Pending Fulfilled Rejected

30. Promise States Pending Fulfilled Rejected Value Reason

31. Promise States Pending Fulfilled Rejected Return Value Thrown Exception

32. Consuming Promises

33. Promise Prototype Methods

34. getJSON('/comments')! .then(onFulfilled, onRejected) Promise.prototype.then

35. getJSON('/comments')! .then(function(comments) {! if (comments) return 'Good'! else throw new

    Error('Bad')! }, function(reason) {! // handle getJSON errors! }) Promise.prototype.then

36. getJSON('/comments')! .then(fulfillOne, rejectOne)! .then(fulfillTwo)! .then(null, rejectTwo) Promise.prototype.then

37. getJSON('/comments')! .then(fulfillOne, rejectOne)! .then(fulfillTwo)! .then(null, rejectTwo) Promise.prototype.then THROW

38. getJSON('/comments')! .then(fulfillOne, rejectOne)! .then(fulfillTwo)! .then(null, rejectTwo) Promise.prototype.then THROW

39. getJSON onFulfilled onRejected getJSON onFulfilled onRejected

40. getJSON('/comments') // waiting...! .then(extractFirstId)! .then(getCommentById) // waiting...! .then(showComment) Promise.prototype.then

41. var promise = getJSON('/comments');! somethingElse();! promise.then(onFulfilled, onRejected); Promise.prototype.then

42. getJSON('/comments')! .then(null, onRejected) Promise.prototype.catch

43. getJSON('/comments')! .catch(onRejected) Promise.prototype.catch

44. Promise Static Methods

45. Promise.cast('Hi you!')! .then(onFulfilled, onRejected) Promise.cast

46. Promise.cast(seededRandom(42))! .then(onFulfilled, onRejected) Promise.cast

47. Promise.cast($.ajax(config))! .then(onFulfilled, onRejected) Promise.cast

48. $.ajax(config)! .then(onFulfilled, onRejected)

49. $.ajax(config)! .then(onFulfilled, onRejected) Lies, all LIES!

50. Promise.cast($.ajax(config))! .then(onFulfilled, onRejected) Promise.cast

51. var promises = [ getJSON('/a'),! getJSON('/b'), getJSON('/c') ]! ! Promise.all(promises)!

    .then(allFulfilled, firstRejected) Promise.all

52. var promises = [ getJSON('/a'),! 'Hi you!', 42, getJSON('/c') ]!

    ! Promise.all(promises)! .then(allFulfilled, firstRejected) Promise.all

53. var promises = [ saveTo(server1),! saveTo(server2), saveTo(server3) ]! ! Promise.race(promises)!

    .then(firstFulfilled, firstRejected) Promise.race

54. Creating Promises

55. new Promise()

56. function() {! var name = prompt('Your name?')! if (!name)! throw

    new Error('Rude user!')! else! return name! } new Promise()

57. new Promise(function(fulfill, reject) {! var name = prompt('Your name?')! if

    (!name)! throw new Error('Rude user!')! else! return name! }) new Promise()

58. new Promise(function(fulfill, reject) {! var name = prompt('Your name?')! if

    (!name)! reject(new Error('Rude user!'))! else! fulfill(name)! }) new Promise()

59. Shortcuts

60. new Promise(function(fulfill, reject) {! fulfill(something)! }) Promise.resolve()

61. new Promise(function(fulfill, reject) {! fulfill(something)! })! Promise.resolve(something) Promise.resolve()

62. new Promise(function(fulfill, reject) {! reject(something)! }) Promise.reject()

63. new Promise(function(fulfill, reject) {! reject(something)! })! Promise.reject(something) Promise.reject()

64. Advanced Techniques

65. this.get('name') // 'Kerrick'! ! getJSON('/comments')! .then(function(comments) {! this.get('name') // throws!

    }) this and bind()

66. this.get('name') // 'Kerrick'! var self = this! getJSON('/comments')! .then(function(comments) {!

    self.get('name') // 'Kerrick'! }) this and bind()

67. this.get('name') // 'Kerrick'! ! getJSON('/comments')! .then(function(comments) {! this.get('name') // 'Kerrick'!

    }.bind(this)) this and bind()

68. getJSON('/comments')! .then(function(comments) {! throw new Error('Hello?')! }) Absorbed Rejections

69. getJSON('/comments')! .then(function(comments) {! throw new Error('Hello?')! })! .catch(console.error.bind(console)) Absorbed Rejections

70. getStudent(name) // <Promise>! .then(getLatestGrade)! .then(log)! .catch(logError)! .then(logOut) Promise-aware Functions

71. log(getLatestGrade(getStudent(name)))! .catch(logError)! .then(logOut) Promise-aware Functions

72. function getLatestGrade(promise) {! return Promise.cast(promise)! .then(function(value) {! // getLatestGrade Logic!

    })! } Promise-aware Functions