mithril-vndb/promise/polyfill.js

"use strict"
/** @constructor */
var PromisePolyfill = function(executor) {
	if (!(this instanceof PromisePolyfill)) throw new Error("Promise must be called with 'new'.")
	if (typeof executor !== "function") throw new TypeError("executor must be a function.")

	var self = this, resolvers = [], rejectors = [], resolveCurrent = handler(resolvers, true), rejectCurrent = handler(rejectors, false)
	var instance = self._instance = {resolvers: resolvers, rejectors: rejectors}
	var callAsync = typeof setImmediate === "function" ? setImmediate : setTimeout
	function handler(list, shouldAbsorb) {
		return function execute(value) {
			var then
			try {
				if (shouldAbsorb && value != null && (typeof value === "object" || typeof value === "function") && typeof (then = value.then) === "function") {
					if (value === self) throw new TypeError("Promise can't be resolved with itself.")
					executeOnce(then.bind(value))
				}
				else {
					callAsync(function() {
						if (!shouldAbsorb && list.length === 0) console.error("Possible unhandled promise rejection:", value)
						for (var i = 0; i < list.length; i++) list[i](value)
						resolvers.length = 0, rejectors.length = 0
						instance.state = shouldAbsorb
						instance.retry = function() {execute(value)}
					})
				}
			}
			catch (e) {
				rejectCurrent(e)
			}
		}
	}
	function executeOnce(then) {
		var runs = 0
		function run(fn) {
			return function(value) {
				if (runs++ > 0) return
				fn(value)
			}
		}
		var onerror = run(rejectCurrent)
		try {then(run(resolveCurrent), onerror)} catch (e) {onerror(e)}
	}

	executeOnce(executor)
}
PromisePolyfill.prototype.then = function(onFulfilled, onRejection) {
	var self = this, instance = self._instance
	function handle(callback, list, next, state) {
		list.push(function(value) {
			if (typeof callback !== "function") next(value)
			else try {resolveNext(callback(value))} catch (e) {if (rejectNext) rejectNext(e)}
		})
		if (typeof instance.retry === "function" && state === instance.state) instance.retry()
	}
	var resolveNext, rejectNext
	var promise = new PromisePolyfill(function(resolve, reject) {resolveNext = resolve, rejectNext = reject})
	handle(onFulfilled, instance.resolvers, resolveNext, true), handle(onRejection, instance.rejectors, rejectNext, false)
	return promise
}
PromisePolyfill.prototype.catch = function(onRejection) {
	return this.then(null, onRejection)
}
PromisePolyfill.prototype.finally = function(callback) {
	return this.then(
		function(value) {
			return PromisePolyfill.resolve(callback()).then(function() {
				return value
			})
		},
		function(reason) {
			return PromisePolyfill.resolve(callback()).then(function() {
				return PromisePolyfill.reject(reason);
			})
		}
	)
}
PromisePolyfill.resolve = function(value) {
	if (value instanceof PromisePolyfill) return value
	return new PromisePolyfill(function(resolve) {resolve(value)})
}
PromisePolyfill.reject = function(value) {
	return new PromisePolyfill(function(resolve, reject) {reject(value)})
}
PromisePolyfill.all = function(list) {
	return new PromisePolyfill(function(resolve, reject) {
		var total = list.length, count = 0, values = []
		if (list.length === 0) resolve([])
		else for (var i = 0; i < list.length; i++) {
			(function(i) {
				function consume(value) {
					count++
					values[i] = value
					if (count === total) resolve(values)
				}
				if (list[i] != null && (typeof list[i] === "object" || typeof list[i] === "function") && typeof list[i].then === "function") {
					list[i].then(consume, reject)
				}
				else consume(list[i])
			})(i)
		}
	})
}
PromisePolyfill.race = function(list) {
	return new PromisePolyfill(function(resolve, reject) {
		for (var i = 0; i < list.length; i++) {
			list[i].then(resolve, reject)
		}
	})
}

module.exports = PromisePolyfill