再看JavaScript異步編程這本書，然后看到了一段代碼var webSocketCache = {};function openWebSocket(serverAddress, callback) {    var socket;    if (serverAddress in webSocketCache) {        socket = webSocketCache[serverAddress];        if (socket.readyState === WebSocket.OPEN) {            callback();        } else {            socket.onopen = _.compose(callback, socket.onopen);        };    } else {        socket = new WebSocket(serverAddress);        webSocketCache[serverAddress] = socket;        socket.onopen = callback;    };    return socket;};書中說        var socket=openWebSocket(url,function(){          socket.send('Hello,server!');              });這樣會使代碼崩潰，不解。。在返回值之前調(diào)用回調(diào)函數(shù)為什么會使代碼崩潰。希望大大們能幫我解釋解釋