js全选反选

DOCTYPE html>
html>
    head>
        meta charset="utf-8">
        title>title>
    head>
    body>
        div>
            input type="checkbox" name="checkboxs" id="" value="咕咕" />咕咕br>
            input type="checkbox" name="checkboxs" id="" value="嘎嘎" />嘎嘎br>
            input type="checkbox" name="checkboxs" id="" value="嘟嘟" />嘟嘟br>
            input type="button" id="quanxuan" value="全选" />
            input type="button" id="quanbuxuan" value="全不选" />
            input type="button" id="fanxuan" value="反选" />
        div>
        script type="text/javascript">
            var checkboxs = document.getElementsByName("checkboxs");
            
            document.getElementById("quanxuan").onclick=function(){
                for(var i=0;icheckboxs.length;i++){
                    checkboxs[i].checked = true;
                }
            }
            document.getElementById("quanbuxuan").onclick=function(){
                for(var i=0;icheckboxs.length;i++){
                    checkboxs[i].checked = false;
                }
            }
            document.getElementById("fanxuan").onclick=function(){
                for(var i=0;icheckboxs.length;i++){
                    checkboxs[i].checked = !checkboxs[i].checked;
                }
            }
            
        script>
    body>
html>