1 | <a href="http://promises-aplus.github.com/promises-spec"><img src="http://promises-aplus.github.com/promises-spec/assets/logo-small.png" alt="Promises/A+ logo" align="right" /></a>
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2 |
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3 | [![Build Status](https://travis-ci.org/cujojs/when.svg?branch=master)](https://travis-ci.org/cujojs/when)
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4 |
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5 | when.js
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6 | =======
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7 |
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8 | When.js is a rock solid, battle-tested [Promises/A+](http://promises-aplus.github.com/promises-spec) and `when()` implementation, including a complete [ES6 Promise shim](docs/es6-promise-shim.md). It's a powerful combination of small size, high performance, debuggability, and rich features:
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9 |
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10 | * Resolve arrays and hashes of promises, as well as infinite promise sequences
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11 | * Execute tasks in parallel or sequentially
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12 | * Transform Node-style and other callback-based APIs into promise-based APIs
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13 |
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14 | When.js is one of the many stand-alone components of [cujoJS](http://cujojs.com), the JavaScript Architectural Toolkit.
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15 |
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16 | Check it out:
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17 |
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18 | - [What's new](CHANGES.md)
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19 | - [API docs](docs/api.md#api)
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20 | - Read more about how [promises simplify async programming](http://know.cujojs.com/tutorials/async/simplifying-async-with-promises)
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21 |
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22 | Installation
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23 | ------------
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24 |
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25 | #### AMD
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26 |
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27 | Availble as `when` through [bower](http://bower.io), or just clone the repo and load `when.js` from the root.
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28 |
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29 | ```
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30 | bower install --save when
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31 | ```
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32 |
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33 | #### CommonJS/Node
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34 |
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35 | ```
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36 | npm install --save when
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37 | ```
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38 |
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39 | [More help & other environments »](docs/installation.md)
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40 |
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41 | Usage
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42 | -----
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43 |
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44 | Promises can be used to help manage complex and/or nested callback flows in a simple manner. To get a better handle on how promise flows look and how they can be helpful, there are a couple examples below (using commonjs).
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45 |
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46 | This first example will print `"hello world!!!!"` if all went well, or `"drat!"` if there was a problem. It also uses [rest](https://github.com/cujojs/rest) to make an ajax request to a (fictional) external service.
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47 |
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48 | ```js
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49 | var rest = require('rest');
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50 |
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51 | fetchRemoteGreeting()
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52 | .then(addExclamation)
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53 | .catch(handleError)
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54 | .done(function(greeting) {
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55 | console.log(greeting);
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56 | });
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57 |
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58 | function fetchRemoteGreeting() {
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59 | // returns a when.js promise for 'hello world'
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60 | return rest('http://example.com/greeting');
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61 | }
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62 |
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63 | function addExclamation(greeting) {
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64 | return greeting + '!!!!'
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65 | }
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66 |
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67 | function handleError(e) {
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68 | return 'drat!';
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69 | }
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70 | ```
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71 |
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72 | The second example shows off the power that comes with when's promise logic. Here, we get an array of numbers from a remote source and reduce them. The example will print `150` if all went well, and if there was a problem will print a full stack trace.
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73 |
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74 | ```js
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75 | var when = require('when');
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76 | var rest = require('rest');
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77 |
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78 | when.reduce(when.map(getRemoteNumberList(), times10), sum)
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79 | .done(function(result) {
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80 | console.log(result);
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81 | });
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82 |
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83 | function getRemoteNumberList() {
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84 | // Get a remote array [1, 2, 3, 4, 5]
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85 | return rest('http://example.com/numbers').then(JSON.parse);
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86 | }
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87 |
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88 | function sum(x, y) { return x + y; }
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89 | function times10(x) {return x * 10; }
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90 | ```
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91 |
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92 | License
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93 | -------
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94 |
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95 | Licensed under MIT. [Full license here »](LICENSE.txt)
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96 |
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97 | Contributing
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98 | ------------
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99 |
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100 | Please see the [contributing guide](CONTRIBUTING.md) for more information on running tests, opening issues, and contributing code to the project.
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101 |
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102 | References
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103 | ----------
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104 |
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105 | Much of this code was inspired by the async innards of [wire.js](https://github.com/cujojs/wire), and has been influenced by the great work in [Q](https://github.com/kriskowal/q), [Dojo's Deferred](https://github.com/dojo/dojo), and [uber.js](https://github.com/phiggins42/uber.js).
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