[英]Conditionally executing a callback within an asynchronous function call in a for loop
我正在研究一个 function ,它遍历端口列表并在其中一个端口可用时调用其回调。 我不想等待每个端口响应,而是想在所有端口上调用 checkPortStatus function 并在第一个端口返回可用时返回。
以下是可在 node.js 中运行的示例代码:
// Check if a port is open (in use) or closed (available)
function checkPortStatus(port, callback) {
// Simulates real world checking of response from port by returning
// after a random time.
setTimeout(function() {
// Simulates a few closed ports
if (port === 3005 || port === 3006 || port === 3007) {
callback('closed')
}
// Simulates a few open ports
else {
callback('open')
}
}, Math.floor(Math.random() * 200))
}
// Calls callback once any available port is found
function findAnAvailablePort(startPort, endPort, callback) {
var check = function(port) {
checkPortStatus(port, function(status) {
// If a port is 'closed', it's considered available
if (status === 'closed') {
callback(port)
}
})
}
for (var port = startPort; port <= endPort; port++) {
check(port)
}
}
findAnAvailablePort(3000, 3010, function(port) {
console.log('AVAILABLE PORT: ' + port)
});
// Don't exit Node, wait for a response
setTimeout(function() { console.log('FIN') }, 5000)
运行代码的结果:
AVAILABLE PORT: 3005
AVAILABLE PORT: 3007
AVAILABLE PORT: 3006
两个问题:
在 function 之外初始化一些变量应该可以解决问题:
// Calls callback once any available port is found
var hasFoundPort = false;
var checkedPorts = 0;
function findAnAvailablePort(startPort, endPort, callback) {
var check = function(port) {
checkPortStatus(port, function(status) {
checkedPorts++;
// If a port is 'closed', it's considered available
if (status === 'closed' && !hasFoundPort) { // only execute callback once
callback(port)
hasFoundPort = true;
}
if(checkedPorts == endPort - startPort + 1) // checked all ports
console.log('finished checking');
})
}
for (var port = startPort; port <= endPort; port++) {
check(port)
}
}
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