how to get promise result

[wideweide]

function SyncFunction(){ var ret; setTimeout(function(){
ret = "hello"; },3000);

// may be promise.then(res=>ret=res) while(ret === undefined) { require('deasync').sleep(100); } // returns hello with sleep; undefined without return ret;
}

// may be promise.then(res=>ret=res)? but it seems waste time to wait?

is there better method?