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PromiseES5.js
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PromiseES5.js
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/**
* 使用ES5语法实现Promise
* @param {function} callback
*/
function PromiseES5(callback) {
this.status = "pending";
this.value = undefined;
this.cbQueue = []; // 回调队列集合
try {
callback(resolve.bind(this), reject.bind(this));
} catch(error) {
reject.call(this, error);
}
function resolve(value) {
function run() {
if (this.status === "pending") {
// value是Promise类型
if (value instanceof this.constructor) {
var _this = this;
value.then(function(rsp) {
_this.value = rsp;
_this.status = "resolved";
handleQueue.call(_this); // 处理任务队列
}, function(err) {
_this.value = err;
_this.status = "rejected";
handleQueue.call(_this); // 处理任务队列
});
}
// value是含有then函数的对象
else if (value && typeof value.then === "function") {
try {
value.then(resolve.bind(this), reject.bind(this));
} catch(error) {
reject.call(this, error);
}
}
// value是普通数据
else {
this.value = value; // 赋值
this.status = "resolved"; // 改状态
handleQueue.call(this); // 处理任务队列
}
}
}
setTimeout(run.bind(this), 0);
}
function reject(error) {
function run() {
if (this.status === "pending") {
this.value = error;
this.status = "rejected";
handleQueue.call(this); // 处理任务队列
}
}
setTimeout(run.bind(this), 0);
}
// 处理任务队列
function handleQueue() {
var _this = this;
if (this.status === "resolved") {
this.cbQueue.map(function(cbObj) {
// 有回调函数,回调的返回结果,作为下一个Promise的值
if (typeof cbObj.onResolved === "function") {
try {
cbObj.resolve(cbObj.onResolved(_this.value));
} catch(error) {
cbObj.reject(error);
}
}
// 穿透,本次value作为下一个Promise的值
else {
cbObj.resolve(_this.value);
}
});
} else if (this.status === "rejected") {
this.cbQueue.map(function(cbObj) {
// 有回调,回调的返回结果,作为下一个Promise的值,并且新Promise为resolved状态
if (typeof cbObj.onRejected === "function") {
try {
cbObj.resolve(cbObj.onRejected(_this.value));
} catch(error) {
cbObj.reject(error);
}
}
// 穿透,本次error作为下一个Promise的值
else {
cbObj.reject(_this.value);
}
});
}
// 队列置空
this.cbQueue.splice(0);
}
}
PromiseES5.prototype.then = function(onResolved, onRejected) {
var _this = this;
return new this.constructor(function(resolve, reject) {
// 异步
if (_this.status === "pending") {
// 加入队列, 等待执行
_this.cbQueue.push({
onResolved: onResolved,
onRejected: onRejected,
resolve: resolve,
reject: reject
});
}
// 同步成功
else if (_this.status === "resolved") {
// 有回调函数,回调的返回结果,作为下一个Promise的值
if (typeof onResolved === "function") {
try {
resolve(onResolved(_this.value));
} catch(error) {
reject(error);
}
}
// 穿透,本次value作为下一个Promise的值
else {
resolve(_this.value);
}
}
// 同步失败
else if (_this.status === "rejected") {
// 有回调,回调的返回结果,作为下一个Promise的值,并且新Promise为resolved状态
if (typeof onRejected === "function") {
try {
resolve(onRejected(_this.value));
} catch(error) {
reject(error);
}
}
// 穿透,本次value作为下一个Promise的值,并且新Promise为rejected状态
else {
reject(_this.value);
}
}
});
}
PromiseES5.prototype.catch = function(onRejected) {
return this.then(null, onRejected);
}
PromiseES5.prototype.finally = function(callback) {
var _this = this;
return this.then(function(rsp) {
callback();
return _this.constructor.resolve(rsp);
}, function(err) {
callback();
return _this.constructor.reject(err);
});
}
PromiseES5.resolve = function(value) {
// value是Primose对象
if (value instanceof this) {
return value;
}
// value是含有then函数的对象
else if (value && typeof value.then === "function") {
return new this(value.then);
}
// value是普通数据
else {
return new this(function(resolve, reject) {
resolve(value);
});
}
}
PromiseES5.reject = function(error) {
return new this(function(resolve, reject) {
reject(error);
});
}
PromiseES5.all = function(promiseList) {
if (!(promiseList instanceof Array)) {
return;
}
var rspList = [];
var count = 0; // 记录rspList中的个数
var _this = this;
return new this(function(resolve, reject) {
for (var i=0, len=promiseList.length; i<len; i++) {
var p = promiseList[i];
// 是Promise类型, 执行then
if (p instanceof _this) {
(function(j) {
p.then(function(rsp) {
rspList[j] = rsp;
if (++count === len) {
// 如果rspList全部返回, 执行resolve
resolve(rspList);
}
}, function(err) {
// 有一个报错, 就执行reject
reject(err);
});
}(i));
}
// 不是Promise类型, 直接作为结果
else {
rspList[i] = p;
if (++count === len) {
// 如果rspList全部返回, 执行resolve
resolve(rspList);
}
}
}
});
}
PromiseES5.race = function(promiseList) {
if (!(promiseList instanceof Array)) {
return;
}
var _this = this;
return new this(function(resolve, reject) {
for (var i=0, len=promiseList.length; i<len; i++) {
var p = promiseList[i];
if (p instanceof _this) {
p.then(function(rsp) {
resolve(rsp);
}, function(err) {
reject(err);
});
}
// 如果不是Promise类型, 直接作为返回结果
else {
resolve(p);
}
}
});
}
PromiseES5.allSettled = function(promiseList) {
if (!(promise instanceof Array)) {
return;
}
var rspList = [];
var count = 0;
var _this = this;
return new this(function(resolve, reject) {
for (var i=0, len=promiseList.length; i<len; i++) {
var p = promiseList[i];
if (p instanceof _this) {
(function(j) {
p.then(function(rsp) {
rspList[j] = rsp;
if (++count === len) {
resolve(rspList);
}
}, function(err) {
rspList[j] = err;
if (++count === len) {
resolve(rspList);
}
});
}(i))
} else {
rspList[i] = p;
if (++count === len) {
resolve(rspList);
}
}
}
});
}