有条件地在for循环中执行异步函数调用中的回调

Question

我正在研究一个函数，该函数遍历一个端口列表，并在其中一个端口可用时调用其回调函数。不用等待每个端口响应，我想在所有端口上调用checkPortStatus函数，并在第一个端口恢复可用时返回。

这里的示例代码可运行在Node.js的：

AVAILABLE PORT: 3005 
AVAILABLE PORT: 3007 
AVAILABLE PORT: 3006 

两个问题：

1. 如何调用回调只有一次

   // 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？我只想要匹配的第一个端口返回。

2. 如何检查是否返回所有函数回调？在这个例子中，当所有checkPortStatus返回端口都不可用时，我需要返回。

Answer 1

初始化功能之外的几个变量应该做的伎俩：

// 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) 
    } 
}