设置元素属性值

姓名:<input type="text"/><br/>
    <input type="checkbox" value="A" />A
    <input type="checkbox" value="B" />B
    <input type="checkbox" value="C" />C
    <input type="checkbox" value="D" />D<br/>
    <input type="button" value="click"/>

$(document).ready(function(e) {
     var obj = $(":checkbox:eq(1)");
    obj.prop("checked","checked");
  });

$(document).ready(function(e) {
            var obj = $(":checkbox:eq(3)");
            obj.attr("checked",true);
        });

$(document).ready(function(e) {
            var obj = $(":checkbox:eq(1)")[0];
            obj.checked = "checked";
        });

$(document).ready(function(e) {
            var obj = $(":checkbox:eq(3)")[0];
            obj.setAttribute("checked","checked");
        });