js中Promise的状态探究

1、promise可以处于等待被赋值的等待态(pending)，可以给出值并转换为解决态(resolved)。

2、一旦promise被一个值resolve丢失，它将始终保持这个值不再被resolve丢失。

实例

functionPromise(fn){
varstate='pending';
varvalue;
vardeferred;

functionresolve(newValue){
value=newValue;
state='resolved';

if(deferred){
handle(deferred);
}
}

functionhandle(onResolved){
if(state==='pending'){
deferred=onResolved;
return;
}

onResolved(value);
}

this.then=function(onResolved){
handle(onResolved);
};

fn(resolve);
}