async函数测试

用nodejs写了一个连接mysql的模块db.js

const mysql = require('mysql');
const pool  = mysql.createPool({
  connectionLimit : 10,
  host            : 'localhost',
  user            : 'root',
  password        : 'root',
  database        : 'mydb'

});
 
let db = {};

db.q = function (sql,params) {
    return new Promise((resolve,reject) => {

            // 取出链接
            pool.getConnection(function(err, connection) {
                if (err) {
                  reject(err);
                    return;
                }
                connection.query(sql,params, function (error, results, fields) {
                  // 释放连接
                    connection.release();
                   if(err){
                       reject(err);
                       return;
                   }
                    resolve(results);

                });
            });
        })
}

module.exports = db;

想测试一下是否联通，就写了个test.js

const db = require('../models/db.js');
let a = await db.q('select * from users',[]);
console.log(a);

但是运行是提示错误。如下：

D:\wordspace\test.js:2
let a = await db.q('select * from users',[]);
              ^^

SyntaxError: Unexpected identifier
    at createScript (vm.js:80:10)
    at Object.runInThisContext (vm.js:139:10)
    at Module._compile (module.js:599:28)
    at Object.Module._extensions..js (module.js:646:10)
    at Module.load (module.js:554:32)
    at tryModuleLoad (module.js:497:12)
    at Function.Module._load (module.js:489:3)
    at Function.Module.runMain (module.js:676:10)
    at startup (bootstrap_node.js:187:16)
    at bootstrap_node.js:608:3

思不得其解，经反复搜索，发现db.js返回的是一个pormise对象，自己用await来接的话，就应当有一个async函数。于是重写测试案例。问题解决

const db = require('../models/db.js');

fn = async ctx => {
    let user = await db.q('select * from users',[]);
    console.log(user);
   }

fn();

测试结果：

D:\wordspace\test.js
[ RowDataPacket { id: 1, username: 'zhangsan', passward: '123456' },
  RowDataPacket { id: 2, username: 'lisi', passward: '234567' } ]

可见异步函数，测试例子是不同，要注意。

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