手写Promise核心代码 - JavaScript前端Web工程师
```
const { reject } = require("core-js/fn/promise");
class Commitment {
static PENDING = '待定';
static FULFILLED = '成功';
static REJECTED = '拒绝';
constructor(func){
this.status = Commitment.PENDING;
this.result = null;
this.resolveCallbacks = [];
this.rejectCallbacks = [];
//***bind(this) 将this指向新创建的对象 commitment ****/
//func(this.resolve.bind(this), this.reject.bind(this));
//原生promise调用than 可以把错误的信息做为内容输出出来 调用方式如下
/***
* let promise = new Promise((resolve, reject) => {
* throw new Error('输出错误信息');
* })
* ** */
try{
func(this.resolve.bind(this), this.reject.bind(this));
} catch (error){
//这里是直接执行不是创建实例后再执行 不用绑定this
this.reject(error);
}
}
resolve(){
setTimeout(() => {
if(this.status === Commitment.PENDING){
this.status = Commitment.FULFILLED;
this.result = result;
this.resolveCallbacks.forEach(callback =>{
callback(result)
})
}
});
}
reject(){
setTimeout(() => {
if(this.status === Commitment.PENDING){
this.status = Commitment.REJECTED;
this.result = result;
this.rejectCallbacks.forEach(callback => {
callback(result)
})
}
});
}
than(onFULFILLED, onREJECTED){
//为实现 .than链式调用 方法内返回new Commitment
return new Commitment((resolve, reject) => {
// than 里面的两个参数不是函数则不被执行
//解决思路 赋值空函数
onFULFILLED = typeof onFULFILLED === 'function' ? onFULFILLED : () => {};
onREJECTED = typeof onREJECTED === 'function' ? onREJECTED : () => {};
if(this.status === Commitment.PENDING){
this.resolveCallbacks.push(onFULFILLED);
this.rejectCallbacks.push(onREJECTED);
}
if(this.status === Commitment.FULFILLED){
onFULFILLED(this.result);
}
if(this.status === Commitment.REJECTED){
onREJECTED(this.result);
}
})
}
}
let commitment = new Commitment((resolve, reject) => {
resolve('这次一定');
});
commitment.than(
result => {console.log(result)},
result => {console.log(result.message)}
).than(
result => {console.log(result)},
result => {console.log(result.message)}
);
```
