Javascript 调试打印未按顺序进行
在下面的代码中,我注意到一个让我困惑的异常现象。打印字符串entryname在somestr打印字符串之前执行。我能知道为什么会这样吗Javascript 调试打印未按顺序进行,javascript,node.js,Javascript,Node.js,在下面的代码中,我注意到一个让我困惑的异常现象。打印字符串entryname在somestr打印字符串之前执行。我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 +
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);
NodeJs本质上是Aysnc,如果异步任务正在执行,NodeJs将把该代码推送到堆栈并执行下一个可用语句 同样的事情也在这里发生
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) {
///
});
在这一部分执行db I/O时,NodeJs将其推送到堆栈并执行下一个console语句
现在,当db调用完成时,它将执行相应的块。log'entryname为'+entry.name 您需要首先了解node.js的异步性质。查询代码中存在SQL注入漏洞。按照我的理解,在回调函数中检索值可以解决我的问题。@AKX,感谢您指出SQL注入漏洞。我将使用参数化查询来修复它们。