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"Promisify" a business object using an internal queue to serialize async operations
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| var when = require('when'); | |
| var delay = require('when/delay'); | |
| var slice = Array.prototype.slice; | |
| var promisePrototype = Object.getPrototypeOf(when.resolve()); | |
| //--------------------------------------------------------- | |
| // A simple business object | |
| //--------------------------------------------------------- | |
| function MyObj() { | |
| this._queue = when.resolve(); | |
| this.value = 0; | |
| } | |
| //--------------------------------------------------------- | |
| // MyObj's prototype | |
| // We'll promisify this and then set it as MyObj's prototype | |
| // These methods are allowed to return promises | |
| //--------------------------------------------------------- | |
| var methods = { | |
| call1: function(x) { | |
| // Implement call1 with whatever business logic you need | |
| console.log('call1 business logic', x); | |
| this.value += x; | |
| return this.value; | |
| }, | |
| call2: function(x) { | |
| // Implement call2 with whatever business logic you need | |
| console.log('call2 business logic', x); | |
| this.value += x; | |
| // For fun, return a delayed value | |
| return delay(1000).yield(this.value); | |
| }, | |
| call3: function(x) { | |
| // Implement call3 with whatever business logic you need | |
| console.log('call3 business logic', x); | |
| this.value += x; | |
| return this.value; | |
| } | |
| }; | |
| //--------------------------------------------------------- | |
| // Set MyObj's prototype by creating queueing versions of its | |
| // methods, and then adding the promise API (then, otherwise, etc.) | |
| // to provide access to the current queue value. | |
| //--------------------------------------------------------- | |
| MyObj.prototype = mixinPromiseMethods(makeQueuedMethods(methods), promisePrototype); | |
| //--------------------------------------------------------- | |
| // Here's how you can use it | |
| //--------------------------------------------------------- | |
| var ob = new MyObj() | |
| ob.call1(1) | |
| .call2(2) | |
| .call3(3) | |
| .then( function(result) { console.log( result ); }) | |
| .otherwise( function(err) { console.log( err ); }); | |
| //--------------------------------------------------------- | |
| // Helpers for promisifying methods and adding promise API | |
| //--------------------------------------------------------- | |
| // Promisify business logic methods | |
| function makeQueuedMethods(methods) { | |
| return Object.keys(methods).reduce(function (prototype, methodName) { | |
| prototype[methodName] = function () { | |
| var args = slice.call(arguments); | |
| var self = this; | |
| this._queue = when(this._queue, function () { | |
| return methods[methodName].apply(self, args); | |
| }); | |
| return this; | |
| }; | |
| return prototype; | |
| }, {}); | |
| } | |
| // Add promise API, routing to internal queue | |
| function mixinPromiseMethods(prototype, promisePrototype) { | |
| return Object.keys(promisePrototype).reduce(function(prototype, methodName) { | |
| prototype[methodName] = function() { | |
| return this._queue[methodName].apply(this._queue, slice.call(arguments)); | |
| }; | |
| return prototype; | |
| }, prototype); | |
| } | |
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