Promise
實(shí)現(xiàn)一個(gè)符合 Promise/A+ 規(guī)范的 MyPromise秒际，并實(shí)現(xiàn) resolve悬赏、reject、all娄徊、race闽颇、defer、deferred等靜態(tài)方法寄锐。
MyPromise
作用：創(chuàng)建
MyPromise實(shí)例兵多。PromiseMyPromise接收一個(gè)回掉函數(shù)
executor-
MyPromise狀態(tài)
-
pending
- 可以轉(zhuǎn)換成 fulfilled 或 rejected
-
fulfilled
- 不可改變成其他狀態(tài)
-
rejected
- 不可改變成其他狀態(tài)
-
-
onFulfilledCallbacks和onRejectedCallbacks兩個(gè)數(shù)組，數(shù)組每一項(xiàng)是一個(gè)函數(shù)橄仆。分別接收
then里面的第一個(gè)參數(shù)和第二個(gè)參數(shù)剩膘。狀態(tài)是
pending的回掉函數(shù)。
-
resolve
promise的狀態(tài)是fulfilled異常是的處理函數(shù)-
接收
value參數(shù)如果是
promise盆顾，執(zhí)行then怠褐。如果不是
promise，把value做為參數(shù)傳給onFulfilledCallbacks里的每個(gè)函數(shù)您宪。
-
reject
promise的狀態(tài)是rejected異常是的處理函數(shù)接收
reason參數(shù)奈懒，把reason做為參數(shù)傳給onRejectedCallbacks里的每個(gè)函數(shù)奠涌。
執(zhí)行
executor，如果有異常筐赔，拋給reject因?yàn)?code>Promise是在同步代碼執(zhí)行完成后再執(zhí)行铣猩，所以要把
Mypromise的執(zhí)行方法resolve和reject放在異步隊(duì)列里
function MyPromise(executor) {
if (typeof executor !== 'function') {
throw new TypeError('Promise resolver ' + executor + ' is not a function');
}
let self = this;
this.status = 'pending';
this.value = undefined;
this.reason = undefined;
this.onFulfilledCallbacks = [];
this.onRejectedCallbacks = [];
function resolve(value) {
if (value instanceof MyPromise) {
return value.then(resolve, reject);
}
if (self.status === 'pending') {
self.value = value;
self.status = 'fulfilled';
self.onFulfilledCallbacks.forEach(item => item(value));
}
}
function reject(reason) {
if (self.status === 'pending') {
self.reason = reason;
self.status = 'rejected';
self.onRejectedCallbacks.forEach(item => item(reason));
}
}
try {
executor(resolve, reject);
} catch (e) {
reject(e);
}
}
MyPromise.prototype.then
作用：接收兩個(gè)函數(shù)參數(shù)，第一個(gè)函數(shù)的參數(shù)是
resolve傳入的參數(shù)茴丰，第二個(gè)參數(shù)是reject傳入的參數(shù)达皿。Promise#then-
onFulfilledMyPromise成功時(shí)執(zhí)行的方法resolve的參數(shù)會(huì)作為value傳給onFulfilled
-
onRejectedMyPromise失敗時(shí)執(zhí)行的方法reject的參數(shù)會(huì)作為value傳給onRejected
返回一個(gè)
MyPromise實(shí)例newPromise，方便鏈?zhǔn)秸{(diào)用-
對(duì)三種狀態(tài)分別處理
每個(gè)狀態(tài)中創(chuàng)建
newPromise-
fulfilled直接執(zhí)行
onFulfilled贿肩，返回值x把
newPromise峦椰、x以及newPromise里的resolve、reject做為參數(shù)傳給resolutionPromise把 MyPromise 的參數(shù)放在異步隊(duì)列里
-
rejected直接執(zhí)行
onRejected汰规，返回值x把
newPromise汤功、x以及newPromise里的resolve、reject做為參數(shù)傳給resolutionPromise把 MyPromise 的參數(shù)放在異步隊(duì)列里
-
pending- 狀態(tài)待定溜哮，把
fulfilled和rejected里的異步函數(shù)分別加到onFulfilledCallbacks和onRejectedCallbacks的最后一位
- 狀態(tài)待定溜哮，把
resolutionPromise后面細(xì)說用
catch捕獲異常滔金，執(zhí)行reject
MyPromise.prototype.then = function (onFulfilled, onRejected) {
let self = this;
typeof onFulfilled !== 'function' && (onFulfilled = function (value) {
return value;
});
typeof onRejected !== 'function' && (onRejected = function (reason) {
throw reason;
});
let newPromise;
/**
* 分別處理實(shí)例的三種狀態(tài)
*/
if (self.status === 'fulfilled') {
newPromise = new MyPromise(function (resolve, reject) {
setTimeout(function () {
try {
let x = onFulfilled(self.value);
resolutionPromise(newPromise, x, resolve, reject);
} catch (e) {
reject(e);
}
});
});
}
if (self.status === 'rejected') {
newPromise = new MyPromise(function (resolve, reject) {
setTimeout(function () {
try {
let x = onRejected(self.reason);
resolutionPromise(newPromise, x, resolve, reject);
} catch (e) {
reject(e);
}
});
});
}
if (self.status === 'pending') {
newPromise = new MyPromise(function (resolve, reject) {
self.onFulfilledCallbacks.push(function (value) {
setTimeout(function () {
try {
let x = onFulfilled(value);
resolutionPromise(newPromise, x, resolve, reject);
} catch (e) {
reject(e);
}
});
});
self.onRejectedCallbacks.push(function (reason) {
setTimeout(function () {
try {
let x = onRejected(reason);
resolutionPromise(newPromise, x, resolve, reject);
} catch (e) {
reject(e);
}
});
});
});
}
return newPromise;
};
MyPromise.prototype.catch
作用：捕獲異常
返回
MyPromise
MyPromise.prototype.catch = function (onRejected) {
return this.then(undefined, onRejected);
};
The Promise Resolution Procedure
Promise解析過程，是以一個(gè)
promise茂嗓、一個(gè)值x及resolve,reject做為參數(shù)的抽象過程promise等于x餐茵，reject拋出異常new TypeError('循環(huán)引用')x如果不是對(duì)象（不包括null）或者函數(shù)，執(zhí)行resolve(x)-
獲取
x.then賦值給then-
then如果是function把
x做為this調(diào)用then述吸，第一個(gè)參數(shù)是resolvePromise忿族，第二個(gè)參數(shù)是rejectPromiseresolvePromise和rejectPromise只有第一次調(diào)用有效resolvePromise參數(shù)為y，執(zhí)行resolutionPromise(promise, y, resolve, reject)rejectPromise參數(shù)為r蝌矛，執(zhí)行reject(r)
-
then如果不是function- 執(zhí)行
resolve(x)
- 執(zhí)行
-
-
用捕獲上一步的異常
執(zhí)行
reject(e)如果執(zhí)行過
resolvePromise或rejectPromise道批，忽略
function resolutionPromise(promise, x, resolve, reject) {
if (promise === x) {
reject(new TypeError('循環(huán)引用'));
}
let then, called;
if (x !== null && (typeof x === 'object' || typeof x === 'function')) {
try {
then = x.then;
if (typeof then === 'function') {
then.call(x, function (y) {
if (called)
return;
called = true;
resolutionPromise(promise, y, resolve, reject);
}, function (r) {
if (called)
return;
called = true;
reject(r);
})
} else {
resolve(x);
}
} catch (e) {
if (called)
return;
reject(e);
}
} else {
resolve(x);
}
}
MyPromise 靜態(tài)方法
MyPromise.all
- 作用：Promise.all
MyPromise.all = function (promises) {
let called = false;
return new MyPromise(function (resolve, reject) {
let newArr = [], count = 0;
for (let i = 0; i < promises.length; i++) {
let item = promises[i];
if (!(item instanceof MyPromise)) {
item = MyPromise.resolve(item);
}
item.then(function (data) {
if (!called) {
newArr[i] = data;
if (i == count) {
resolve(newArr);
count++;
}
}
}, function (e) {
if (!called) {
reject(e);
called = true;
}
});
}
});
};
MyPromise.race
- 作用：Promise.race
MyPromise.race = function (promises) {
return new MyPromise(function (resolve, reject) {
let called = false;
for (let i = 0; i < promises.length; i++) {
let item = promises[i];
if (!(item instanceof MyPromise)) {
item = MyPromise.resolve(item);
}
item.then(function (data) {
if (!called) {
resolve(data);
called = true;
}
}, function (e) {
if (!called) {
reject(e);
called = true;
}
});
}
})
};
MyPromise.resolve
MyPromise.resolve = function (value) {
if (value instanceof MyPromise) {
return value;
}
return new MyPromise(function (resolve, reject) {
if (typeof value !== null && typeof value === 'object' && typeof value.then === 'function') {
value.then();
} else {
resolve(value);
}
})
};
MyPromise.reject
MyPromise.reject = function (e) {
return new MyPromise(function (resolve, reject) {
reject(e);
})
};
test
npm i -g promises-aplus-tests
promises-aplus-tests Promise.js
