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104 lines (96 loc) · 2.87 KB
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/**
* Created by wyw on 2018/12/17.
*/
function Promise(Fn){
this.value;
this.reason;
this.resolves = [];
this.rejects = [];
this.status = 'PENDING';
if(this.status === 'PENDING') {
let transition = (status, val) => {
setTimeout(_ => {
this.status = status;
let f = status === 'FULFILLED',
queue = this[f ? 'resolves' : 'rejects'];
queue.forEach(fn => val = fn(val) || val);
this[f ? 'value' : 'reason'] = val;
});
};
var resolve = (value) => {
transition('FULFILLED', value);
};
var reject = (reason) => {
transition('REJECTED', reason);
}
}
try {
Fn(resolve, reject);
}
catch(err) {
reject(err);
}
}
Promise.prototype.then = function(onFulfilled, onRejected) {
let promise = this;
return new Promise((resolve, reject) => {
function success(value) {
let val = typeof onFulfilled === 'function' && onFulfilled(value) || value;
if(val && typeof val['then'] === 'function'){ // 判断是否有then方法
val.then(function(value){ // 如果返回的是Promise 则直接执行得到结果后再调用后面的then方法
resolve(value);
},function(reason){
reject(reason);
});
}else{
resolve(val);
}
}
function erro (reason) {
let rea = typeof onRejected === 'function' && onRejected(reason) || reason;
reject(rea);
}
if (promise.status === 'PENDING') {
promise.resolves.push(success);
promise.rejects.push(erro);
} else if (promise.status === 'FULFILLED') {
success(promise.value);
} else if (promise.status === 'REJECTED') {
erro(promise.reason);
}
});
};
Promise.prototype.catch = function(onRejected){
return this.then(null, onRejected);
};
// function getInfo(success, fail) {
// return new Promise((resolve, reject) => {
// setTimeout(_ => {
// let ran = Math.random();
// console.log(success, ran);
// if (ran > 0.5) {
// resolve(success);
// } else {
// reject(fail);
// }
// }, 200);
// })
// }
//
// getInfo('Vchat', 'fail').then(res => {
// console.log('1', res);
// return getInfo('可以线上预览了', 'erro');
// }).catch(err => {
// console.log('2', err);
// }).then(res => {
// console.log('3', res);
// }).catch(err => {
// console.log('4', err);
// });
const p2 = new Promise((resolve, reject) => {
throw new Error('报错了');
})
.then(result => {console.log(result)})
.catch(e => {
console.log(e);
});