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Node.js版Promise实现
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var EventEmitter = require('events').EventEmitter; | |
var util = require('util'); | |
var fs = require('fs'); | |
/** | |
* promise 实现 | |
*/ | |
var Promise = function () { | |
EventEmitter.call(this); | |
}; | |
util.inherits(Promise, EventEmitter); | |
Promise.prototype.then = function (fulfilledHandler, errorHandler) { | |
if (typeof fulfilledHandler === 'function') { | |
this.once('success', fulfilledHandler); | |
} | |
if (typeof errorHandler === 'function') { | |
this.once('error', errorHandler); | |
} | |
return this; | |
}; | |
/** | |
* Deferred 实现 | |
*/ | |
var Deferred = function () { | |
this.state = 'unfulfilled'; | |
this.promise = new Promise(); | |
}; | |
Deferred.prototype.resolve = function (obj) { | |
this.state = 'fulfilled'; | |
this.promise.emit('success', obj); | |
}; | |
Deferred.prototype.reject = function (obj) { | |
this.state = 'failed'; | |
this.promise.emit('error', obj); | |
}; | |
/** | |
* 实例:文件读取 | |
*/ | |
var readFile = function (filename, encoding) { | |
var deferred = new Deferred(); | |
fs.readFile(filename, encoding, function (err, data) { | |
if (err) { | |
deferred.reject(err); | |
} else { | |
deferred.resolve(data); | |
} | |
}); | |
return deferred.promise; | |
}; | |
readFile('filename', 'utf8').then(function (data) { | |
console.log(this.state); // filfulled | |
}, function (err) { | |
console.log(this.state); // failed | |
}); |
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