基于ES6语法手写promise A 规范，源码实现
代码语言：javascript复制class Promise {
constructor(excutorCallBack) {
this.status = 'pending';
this.value = undefined;
this.fulfilledAry = [];
this.rejectedAry = [];
//=>执行EXCUTOR（异常捕获）
let resolveFn = result => {
let timer = setTimeout(() => {
clearTimeout(timer);
if (this.status !== 'pending') return;
this.status = 'fulfilled';
this.value = result;
this.fulfilledAry.forEach(item => item(this.value));
}, 0);
};
let rejectFn = reason => {
let timer = setTimeout(() => {
clearTimeout(timer);
if (this.status !== 'pending') return;
this.status = 'rejected';
this.value = reason;
this.rejectedAry.forEach(item => item(this.value));
}, 0);
};
try {
excutorCallBack(resolveFn, rejectFn);
} catch (err) {
//=>有异常信息按照REJECTED状态处理
rejectFn(err);
}
}
then(fulfilledCallBack, rejectedCallBack) {
//=>处理不传递的状况
typeof fulfilledCallBack !== 'function' ? fulfilledCallBack = result => result : null;
typeof rejectedCallBack !== 'function' ? rejectedCallBack = reason => {
throw new Error(reason instanceof Error ? reason.message : reason);
} : null;
//=>返回一个新的PROMISE实例
return new Promise((resolve, reject) => {
this.fulfilledAry.push(() => {
try {
let x = fulfilledCallBack(this.value);
x instanceof Promise ? x.then(resolve, reject) : resolve(x);
} catch (err) {
reject(err);
}
});
this.rejectedAry.push(() => {
try {
let x = rejectedCallBack(this.value);
x instanceof Promise ? x.then(resolve, reject) : resolve(x);
} catch (err) {
reject(err);
}
});
});
}
catch(rejectedCallBack) {
return this.then(null, rejectedCallBack);
}
static all(promiseAry = []) {//=>Promise.all()
return new Promise((resolve, reject) => {
//=>INDEX:记录成功的数量 RESULT:记录成功的结果
let index = 0,
result = [];
for (let i = 0; i < promiseAry.length; i ) {
//=>promiseAry[i]:
//每一个需要处理的PROMISE实例
promiseAry[i].then(val => {
index ;
result[i] = val;//=>索引需要和promiseAry对应上，保证结果的顺序和数组顺序一致
if (index === promiseAry.length) {
resolve(result);
}
}, reject);
}
});
}
}
module.exports = Promise;
