function TestPromise(fn){
let callbacks=[],value=null,state='pending',setTime;
resolve=function(newValue){
value=newValue;
state='resolved';
execute()
}
reject=function(newValue){
value=newValue;
state='rejected';
execute();
}
execute=function(){//把promise 放入宏任务执行，比then执行慢
setTime&&clearTimeout(setTime);
setTime=setTimeout(()=>{
while (callbacks.length>0) {
callbacks.shift()(value)
}
},0)
}
this.then=function(resolved,rejected){
if(state=='pending'){ //同步时候比resolve 执行更快
callbacks=[...callbacks,...[resolved,rejected]].filter(v=>!!v);
}else if(state=='resolved'){ //当状态发生更改的时候,执行成功||失败函数
resolved(value)
}else if(state=='rejected'){
rejected(value)
}
return this
}
fn(resolve,reject)
}
new TestPromise((resolve)=>{ setTimeout(()=>{ resolve('1') },100) }).then(v=>{ console.log(v,'--------1') },()=>{ console.log('--------2') }).then((e)=>{ console.log(e) },)