js闭包的一个小问题

function a(){  
    var b = 1;  
      
    window.setTimeout(function(){ //用定时器来触发就不搞按钮啦  
        alert(b);  
    },3000);  
      
      
}  
a();  

function a(){  
    var b = 1;  
      
    window.setTimeout(function(){<span style="font-family: Arial, Helvetica, sans-serif;">//用定时器来触发就不搞按钮啦</span>  
  
        alert(b);  
        var b = 2;  
    },3000);  
      
      
}  
a();