js 報錯 Illegal break statement

var a = {"a":1,"b":2,"c":3};
var flag=0;
for(var i in a){
    $.ajax({
        type:'GET',
        url:'a.php',
        success:function(){
            if(i=="b"){
                alert(a[i]);
                break;
            }
        }
    })
}

break 不能用在 function 裏