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miniapp promise
var PENDING = 'pending'
var SEALED = 'sealed'
var FULFILLED = 'fulfilled'
var REJECTED = 'rejected'
var NOOP = function(){}
function isArray(value) {
return Object.prototype.toString.call(value) === '[object Array]'
}
// async calls
var asyncSetTimer = typeof setImmediate !== 'undefined' ? setImmediate : setTimeout
var asyncQueue = []
var asyncTimer
function asyncFlush(){
// run promise callbacks
for (var i = 0; i < asyncQueue.length; i++)
asyncQueue[i][0](asyncQueue[i][1])
// reset async asyncQueue
asyncQueue = []
asyncTimer = false
}
function asyncCall(callback, arg){
asyncQueue.push([callback, arg])
if (!asyncTimer)
{
asyncTimer = true
asyncSetTimer(asyncFlush, 0)
}
}
function invokeResolver(resolver, promise) {
function resolvePromise(value) {
resolve(promise, value)
}
function rejectPromise(reason) {
reject(promise, reason)
}
try {
resolver(resolvePromise, rejectPromise)
} catch(e) {
console.log(e.stack)
rejectPromise(e)
}
}
function invokeCallback(subscriber){
var owner = subscriber.owner
var settled = owner.state_
var value = owner.data_
var callback = subscriber[settled]
var promise = subscriber.then
if (typeof callback === 'function')
{
settled = FULFILLED
value = callback(value)
}
if (!handleThenable(promise, value))
{
if (settled === FULFILLED)
resolve(promise, value)
if (settled === REJECTED)
reject(promise, value)
}
}
function handleThenable(promise, value) {
var resolved
try {
if (promise === value)
throw new TypeError('A promises callback cannot return that same promise.')
if (value && (typeof value === 'function' || typeof value === 'object'))
{
var then = value.then; // then should be retrived only once
if (typeof then === 'function')
{
then.call(value, function(val){
if (!resolved)
{
resolved = true
if (value !== val)
resolve(promise, val)
else
fulfill(promise, val)
}
}, function(reason){
if (!resolved)
{
resolved = true
reject(promise, reason)
}
})
return true
}
}
} catch (e) {
if (!resolved)
reject(promise, e)
return true
}
return false
}
function resolve(promise, value){
if (promise === value || !handleThenable(promise, value))
fulfill(promise, value)
}
function fulfill(promise, value){
if (promise.state_ === PENDING)
{
promise.state_ = SEALED
promise.data_ = value
asyncCall(publishFulfillment, promise)
}
}
function reject(promise, reason){
if (promise.state_ === PENDING)
{
promise.state_ = SEALED
promise.data_ = reason
asyncCall(publishRejection, promise)
}
}
function publish(promise) {
var callbacks = promise.then_
promise.then_ = undefined
for (var i = 0; i < callbacks.length; i++) {
invokeCallback(callbacks[i])
}
}
function publishFulfillment(promise){
promise.state_ = FULFILLED
publish(promise)
}
function publishRejection(promise){
promise.state_ = REJECTED
publish(promise)
}
/**
* @class
*/
function P(resolver){
if (typeof resolver !== 'function')
throw new TypeError('Promise constructor takes a function argument')
if (this instanceof P === false)
throw new TypeError('Failed to construct \'Promise\': Please use the \'new\' operator, this object constructor cannot be called as a function.')
this.then_ = []
invokeResolver(resolver, this)
}
P.prototype = {
constructor: P,
state_: PENDING,
then_: null,
data_: undefined,
then: function(onFulfillment, onRejection){
var subscriber = {
owner: this,
then: new this.constructor(NOOP),
fulfilled: onFulfillment,
rejected: onRejection
}
if (this.state_ === FULFILLED || this.state_ === REJECTED)
{
// already resolved, call callback async
asyncCall(invokeCallback, subscriber)
}
else
{
// subscribe
this.then_.push(subscriber)
}
return subscriber.then
},
'catch': function(onRejection) {
return this.then(null, onRejection)
}
}
P.all = function(promises){
var Class = this
if (!isArray(promises))
throw new TypeError('You must pass an array to P.all().')
return new Class(function(resolve, reject){
var results = []
var remaining = 0
function resolver(index){
remaining++
return function(value){
results[index] = value
if (!--remaining)
resolve(results)
}
}
for (var i = 0, promise; i < promises.length; i++)
{
promise = promises[i]
if (promise && typeof promise.then === 'function')
promise.then(resolver(i), reject)
else
results[i] = promise
}
if (!remaining)
resolve(results)
})
}
P.race = function(promises){
var Class = this
if (!isArray(promises))
throw new TypeError('You must pass an array to P.race().')
return new Class(function(resolve, reject) {
for (var i = 0, promise; i < promises.length; i++)
{
promise = promises[i]
if (promise && typeof promise.then === 'function')
promise.then(resolve, reject)
else
resolve(promise)
}
})
}
P.resolve = function(value){
var Class = this
if (value && typeof value === 'object' && value.constructor === Class)
return value
return new Class(function(resolve){
resolve(value)
})
}
P.reject = function(reason){
var Class = this
return new Class(function(resolve, reject){
reject(reason)
})
}
module.exports = typeof Promise == 'function' ? Promise : P
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