无法从回调函数内部访问响应

Question

I have a problem finishing a response from within a callback function. The following pared-down code is supposed to check inside a mysql connection query if a table exists and finish the response with this information. But it doesn't. When I access result within the query it seems to be another variable and the result.end() inside it doesn't end the response. Shouldn't be result in the same scope and able to finish my response? How can I achieve my goal?

var formidable = require('formidable'),
    http = require('http'),
    util = require('util'),
    mysql = require('mysql'),
    fs = require('fs'),
    connection = mysql.createConnection({
        host: 'localhost',
        user: 'foo',
        passwort: 'bar'
    });

connection.connect(function (err) {
    if (err)
        throw err;
});

http.createServer(function (request, result) {

    // some request handling

    if (request.url == '/index' && request.method.toLowerCase() == 'get') {
        result.writeHead(200, {
            "Content-Type": "text/plain",
            "Access-Control-Allow-Origin": "*"
        });
        result.write('Response:\n\n');

        // result.end(); <- At this position it would create the expected response.

        connection.query('USE Database', function (err, results) {
            if (err)
                throw err;
            connection.query('SHOW TABLES LIKE "Table"', function(err, results) {
                if (results.length == 0)
                    result.write('table not found');
                result.end(); // <- this one don't
            });
        });
    }
}).listen(8080);

Answer 1

I would rewrite your code to the following:

var http = require('http'),
    mysql = require('mysql'),
    connection = mysql.createConnection({
        host: 'localhost',
        user: 'root',
        password: 'root'
    });

connection.connect(function (err) {
    if (err) {
        throw err;
    }

    console.log('Connected!');
});

http.createServer(function(req, res) {
    connection.query('USE test', function (err, results) {
        if (err) {
            res.end("ERROR from 'USE test'");
        } else {
            connection.query('SHOW TABLES LIKE "Table"', function(err, results) {
                if (results.length == 0) {
                    res.end('table not found');
                } else {
                    res.end('table found!');
                }
            });
        }
    });
}).listen(8080);