关于js语法的疑惑

[qq_33626745]

本人从事java,对js不太熟.

        var ws;
	var target = "ws://127.0.0.1:8080/WebSocketDemo/echo";
	
	function subOpen(){//建立连接
		if (target == '') {
            alert('Please select server side connection implementation.');
            return;
        }

        if ('WebSocket' in window) {
            ws = new WebSocket(target);
            console.info("创建WebSocket对象");
            
            var names="";         
            for(var name in ws){         
               names+=name+": "+ws[name]+",\n";    
            }    
            alert(names);     
        } else if ('MozWebSocket' in window) {
            ws = new MozWebSocket(target);
            console.info("创建MozWebSocket对象");
        } else {
            alert('WebSocket is not supported by this browser.');
            return;
        }
   }     	
  	ws.onmessage=function(event){
		var dv = document.getElementById('dv');
		dv.innerHTML += event.data;
	} 
	
	
	function send(){//发送消息
		var msg = document.getElementById('msg').value;
		console.info("发送消息:"+msg);
		ws.send(msg);//websocket对象的send方法
	 
	}

下面这么写就没有问题:

	var ws;
	var target = "ws://127.0.0.1:8080/WebSocketDemo/echo";
	
	function subOpen(){//建立连接
	if (target == '') {
            alert('Please select server side connection implementation.');
            return;
        }
        if ('WebSocket' in window) {
            ws = new WebSocket(target);
            console.info("创建WebSocket对象");
            
        } else if ('MozWebSocket' in window) {
            ws = new MozWebSocket(target);
            console.info("创建MozWebSocket对象");
        } else {
            alert('WebSocket is not supported by this browser.');
            return;
        }        
	ws.onmessage=function(data){//接收服务器发送的信息
		console.info("接收服务端的数据:"+data.data);
	}; 
	}	
	function send(){//发送消息
		var msg = document.getElementById('msg').value;
		console.info("发送消息:"+msg);
		ws.send(msg);//websocket对象的send方法
	 
	}

[jio可]

f12看下控制台就清楚哪里出错了

[scscms太阳光]

function subOpen(){ ... ws = new WebSocket(target); } ws.onmessage = function(){} //这里就错了，subOpen函数还没有执行，即ws还是nudefined怎么可能有onmenssage方法呢？ 下面的例子很明显是在new　webSocket后再赋值方法