async不返回promise,await关键字等待promise的解析。async是一个增强的生成器函数,await的工作方式有点像yield
我认为语法(我不是百分之百确定)是
async function* getVal() {...}
ES2016生成器函数的工作方式有点像这样。我已经制作了一个数据库处理程序,它基于您这样编程的繁琐之上
db.exec(function*(connection) {
if (params.passwd1 === '') {
let sql = 'UPDATE People SET UserName = @username WHERE ClinicianID = @clinicianid';
let request = connection.request(sql);
request.addParameter('username',db.TYPES.VarChar,params.username);
request.addParameter('clinicianid',db.TYPES.Int,uid);
yield connection.execSql();
} else {
if (!/^\S{4,}$/.test(params.passwd1)) {
response.end(JSON.stringify(
{status: false, passwd1: false,passwd2: true}
));
return;
}
let request = connection.request('SetPassword');
request.addParameter('userID',db.TYPES.Int,uid);
request.addParameter('username',db.TYPES.NVarChar,params.username);
request.addParameter('password',db.TYPES.VarChar,params.passwd1);
yield connection.callProcedure();
}
response.end(JSON.stringify({status: true}));
}).catch(err => {
logger('database',err.message);
response.end(JSON.stringify({status: false,passwd1: false,passwd2: false}));
});
注意我是如何像普通同步那样编程的,特别是在
yield connection.execSql
在
yield connection.callProcedure
exec函数是一个相当典型的基于承诺的生成器
exec(generator) {
var self = this;
var it;
return new Promise((accept,reject) => {
var myConnection;
var onResult = lastPromiseResult => {
var obj = it.next(lastPromiseResult);
if (!obj.done) {
obj.value.then(onResult,reject);
} else {
if (myConnection) {
myConnection.release();
}
accept(obj.value);
}
};
self._connection().then(connection => {
myConnection = connection;
it = generator(connection); //This passes it into the generator
onResult(); //starts the generator
}).catch(error => {
reject(error);
});
});
}