Question

在下面的代码中，我注意到了一个使我感到困惑的异常。打印字符串“ entryname”在“ somestr”打印字符串之前执行。我可能知道为什么会这样吗？

var somestr = "";
con.query(
  'SELECT name,areaid, panellabel,voltageid,installationtypeid from installation, (SELECT companyid from building where name="' +
    req.body.location +
    '")as company where installation.id=company.companyid',
  function(err, rows, fields) {
    if (err) throw err;
    var output = JSON.parse(JSON.stringify(rows));
    var arr = [];
    console.log(rows);
    output.forEach(function(entry) {
      console.log("entryname is " + entry.name);
      somestr =
        somestr +
        "<TR><TD>" +
        entry.name +
        "<TD>" +
        entry.areaid +
        "<TD>" +
        entry.areaid +
        "<TD>" +
        entry.panellabel +
        "<TD>" +
        "<TD>" +
        entry.voltageid +
        "<TD>" +
        entry.installationtypeid;
      console.log(somestr);
    });
  }
);
console.log("somestr is " + somestr + "end somestr");
tablehead = tablehead + somestr;
console.log(somestr);
res.send(tablehead);

Answer 1

NodeJs本质上是Aysnc，如果正在执行异步任务，NodeJS会将该代码压入堆栈并执行下一条可用语句。

这里也发生了同样的事情。

con.query('SELECT name,areaid, panellabel,voltageid,installationtypeid from installation, (SELECT companyid from building where name=\"' + req.body.location + '\")as company where installation.id=company.companyid', function (err, rows, fields) {
  ///
});

此部分正在执行数据库I / O操作，NodeJ将其推入堆栈并执行下一条语句console.log("somestr is " + somestr + "end somestr");

现在，当数据库调用完成时，它将执行相应的块。 console.log('entryname is ' + entry.name);

调试打印没有顺序发生

1 个答案: