错误：throw er; // Unhandled 'error' event

发现是nodejs的过程中遇到了如下的运行错误

events.js:72
        throw er; // Unhandled 'error' event
Error: listen EADDRINUSE
    at errnoException (net.js:901:11)
    at Server._listen2 (net.js:1039:14)
    at listen (net.js:1061:10)
    at Server.listen (net.js:1127:5)
    at Object.<anonymous> (./server/index.js:73:24)
    at Module._compile (module.js:456:26)