在Node.js中完成for循环后,我怎么能运行一个函数? [英] How could I run a function after the completion of a for loop in Node.js?
问题描述
假如我在Node.js中有一个结构如下所示:
Say if I have a structure in Node.js shown below:
for (i = 0; i < 50; i++) {
//Doing a for loop.
}
function after_forloop() {
//Doing a function.
}
after_forloop();
那么我怎样才能确保在forloop完成后触发after_forloop()函数?
So how could I make sure the after_forloop() function is fired after the forloop is completed?
如果你想看看我实际在做什么:
In case if you want to see what I am actually working on:
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello World\n');
}).listen(1337, '127.0.0.1');
console.log('Server running at http://127.0.0.1:1337/');
var proxyChecker = require('proxy-checker');
var fs = require('fs');
function get_line(filename, line_no, callback) {
fs.readFile(filename, function (err, data) {
if (err) throw err;
var lines = data.toString('utf-8').split("\n");
var firstLineBreak = data.toString('utf-8').indexOf("\n");
var originalText = data.toString('utf-8');
var newText = originalText.substr(firstLineBreak + 1);
if(+line_no > lines.length){
return callback('File end reached without finding line', null);
}
callback(null, lines[+line_no], newText);
});
}
for (i = 0; i < 50; i++) {
get_line('proxy_full.txt', i, function(err, line, newText){
fs.appendFile('proxy.txt', line + '\n', function (err) {
if (err) throw err;
});
fs.writeFile('proxy_full.txt', newText, function (err) {
if (err) throw err;
});
})
}
after_forloop();
function after_forloop() {
proxyChecker.checkProxiesFromFile(
// The path to the file containing proxies
'proxy.txt',
{
// the complete URL to check the proxy
url: 'http://google.com',
// an optional regex to check for the presence of some text on the page
regex: /.*/
},
// Callback function to be called after the check
function(host, port, ok, statusCode, err) {
if (ok) {
console.log(host + ':' + port);
fs.appendFile('WorkingProxy.txt', host + ':' + port + '\n', function (err) {
if (err) throw err;
});
}
}
);
setTimeout(function(){
fs.writeFile('proxy.txt', "", function (err) {
if (err) throw err;
});
console.log('Proxy Check Completed.')
process.exit(1);
}, 5000);
}
基本上我想允许节点服务器在列表代理服务器上运行50测试在一个时间(在五秒钟内)。然后服务器应该将工作代理保存到一个新文件。
Basically I like to allow the node server run 50 test on a list proxy servers at a time (within five seconds). And then the server should save the working proxies to a new file.
推荐答案
也许这会有所帮助:
var operationsCompleted = 0;
function operation() {
++operationsCompleted;
if (operationsCompleted === 100) after_forloop();
}
for (var i = 0; i < 50; i++) {
get_line('proxy_full.txt', i, function(err, line, newText){
fs.appendFile('proxy.txt', line + '\n', function (err) {
if (err) throw err;
operation();
});
fs.writeFile('proxy_full.txt', newText, function (err) {
if (err) throw err;
operation();
});
})
}
不可否认,这不是一个优雅的解决方案。如果您正在做很多这样的事情,您可能需要查看 Async.js 之类的内容。
Admittedly this isn't an elegant solution. If you're doing a whole lot of this you might want to check out something like Async.js.
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