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?