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106 lines
2.6 KiB
JavaScript

5 years ago
'use strict';
var asap = require('asap')
module.exports = Promise;
function Promise(fn) {
if (typeof this !== 'object') throw new TypeError('Promises must be constructed via new')
if (typeof fn !== 'function') throw new TypeError('not a function')
var state = null
var value = null
var deferreds = []
var self = this
this.then = function(onFulfilled, onRejected) {
return new self.constructor(function(resolve, reject) {
handle(new Handler(onFulfilled, onRejected, resolve, reject))
})
}
function handle(deferred) {
if (state === null) {
deferreds.push(deferred)
return
}
asap(function() {
var cb = state ? deferred.onFulfilled : deferred.onRejected
if (cb === null) {
(state ? deferred.resolve : deferred.reject)(value)
return
}
var ret
try {
ret = cb(value)
}
catch (e) {
deferred.reject(e)
return
}
deferred.resolve(ret)
})
}
function resolve(newValue) {
try { //Promise Resolution Procedure: https://github.com/promises-aplus/promises-spec#the-promise-resolution-procedure
if (newValue === self) throw new TypeError('A promise cannot be resolved with itself.')
if (newValue && (typeof newValue === 'object' || typeof newValue === 'function')) {
var then = newValue.then
if (typeof then === 'function') {
doResolve(then.bind(newValue), resolve, reject)
return
}
}
state = true
value = newValue
finale()
} catch (e) { reject(e) }
}
function reject(newValue) {
state = false
value = newValue
finale()
}
function finale() {
for (var i = 0, len = deferreds.length; i < len; i++)
handle(deferreds[i])
deferreds = null
}
doResolve(fn, resolve, reject)
}
function Handler(onFulfilled, onRejected, resolve, reject){
this.onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : null
this.onRejected = typeof onRejected === 'function' ? onRejected : null
this.resolve = resolve
this.reject = reject
}
/**
* Take a potentially misbehaving resolver function and make sure
* onFulfilled and onRejected are only called once.
*
* Makes no guarantees about asynchrony.
*/
function doResolve(fn, onFulfilled, onRejected) {
var done = false;
try {
fn(function (value) {
if (done) return
done = true
onFulfilled(value)
}, function (reason) {
if (done) return
done = true
onRejected(reason)
})
} catch (ex) {
if (done) return
done = true
onRejected(ex)
}
}