"Events" caused by single selection in HTML-CSS group

Because of a radio button problem of Death, many people came out to talk nonsense. Alas, this rookie also came out and went to take advantage of the situation. I accidentally touched one.

First, let’s look at a piece of code dug out from baidu, and I will start from here.

Copy the codeThe code is as follows:

<script>  
function checkradio()  
{  
    for(i=0;i<document.;i++)  
    {  
        if(document.[i].checked)  
        {  
alert("Your favorite fruit is:"+document.[i].);
        }  
    }  
}  
</script>  
<form name="form1">  
Your favorite fruit is:<br>
<input type=radio value="Fruit1" name="Fruit" checked>Apple
<input type=radio value="Fruit2" name="Fruit">Banana
<input type=radio value="Fruit3" name="Fruit">Strawberry
<input type=radio value="Fruit4" name="Fruit">Pineapple
<input type=button value="Select" onclick="checkradio()">
</form> 

The purpose of this code is to determine the selected value.

The effect you want now is to give a prompt if each option is empty, and the following code is the effect after some changes.

Program code
<script>
function checkradio()
{
    var j=0;
    for(i=0;i<document.;i++)
    {
        if(document.[i].checked==true)
        {
alert("You selected"+document.[i].);
//break;This break is invalid after Feifei's guidance, and it is removed
        }else{
            j=j+1;
            if(j==4){
alert("Damn, you choose one, I don't have to come out!");
            }
        }
    }
}
</script>
<form name="form1">
Your favorite fruit is:<br>
<input type=radio value="Fruit1" name="Fruit">
apple
<input type=radio value="Fruit2" name="Fruit">Banana
<input type=radio value="Fruit3" name="Fruit">Strawberry
<input type=radio value="Fruit4" name="Fruit">Pineapple
<input type=button value="Select" onclick="checkradio()">
</form>

Later I saw a clearer piece of code written by Chen, so I will post it here too.
(Note: For the sake of ease of testing, I changed it, and the idea is still his idea)

Copy the codeThe code is as follows:

<script>  
function checkradio()  
{  
    var flag=false;  
    for(var i=0;i<=document.-1;i++)  
    {  
          if([i].checked){  
            flag=true;}  
    }  
    if(flag)  
    {  
          alert("^_^");  
          return false;  
    }else{  
alert("Hero, please choose one!");
    }  
}  
</script> 

The single choice was over. Boss Feifei didn't give up and came up with a code for the check box at night.

Copy the codeThe code is as follows:

<script>  
    var j=("Fruit");  
function allche(){  
    for(var i=0; i <; i++){  
            if(document.[i].checked!=true) document.[i].checked= document.;  
            if(document.[i].checked==true) document.[i].checked= document.;  
    }  
}  
function checkall(){  
var aa=0  
    for(var i=0; i <; i++){      
            if(document.[i].checked == true)  aa++;  
             aa!= ? document.=false : document.=true;  
    }  
}  
function checkradio(){  
var a=0  
var list=""  
for(var i=0; i<;i++)  
if (document.[i].checked== true){  
list=="" ? list=document.[i].value : list=list+","+document.[i].value;  
}  
if (list!="") alert("The fruit you like is"+list);

else{  
a++;  
if (a==)alert("Brother. If you don't choose, how can I know what you like?");}
}  

</script>  
<form name="form1" >  
Your favorite fruit is:<br>
<input type=checkbox value="Apple" name="Fruit" onClick="checkall()">
apple
<input type=checkbox value="banana" name="Fruit" onClick="checkall()">
banana
<input type=checkbox value="Strawberry" name="Fruit" onClick="checkall()">
strawberry
<input type=checkbox value="pineapple" name="Fruit" onClick="checkall()">
Pineapple
<input type=button value="Select" onclick="checkradio()">
<input type=checkbox   onclick="allche()" name="suoy">Select all
</form>  

<script language="javascript" type="text/javascript" >  
function test()  
{  
    fruitlist = "";  
    for(i=0;i<("frm").length;i++)  
        if(("frm")[i].type=="checkbox" && ("frm")[i].checked)  
            fruitlist += ("frm")[i].value + " ";  
    if(fruitlist!="")  
alert("Your favorite fruit is"+fruitlist);
    else  
alert("Brother. How do I know what you like if you don't choose?");
}  
</script>  

Let’s have a simpler code and better-effect code about checking.

Copy the codeThe code is as follows:

<SCRIPT LANGUAGE="JavaScript">  
<!-- Begin  
function checkAll() {  
for (var j = 1; j <= 9; j++) {  
box = eval("" + j);   
if ( == false)  = true;  
   }  
}  

function uncheckAll() {  
for (var j = 1; j <= 9; j++) {  
box = eval("" + j);   
if ( == true)  = false;  
   }  
}  

function switchAll() {  
for (var j = 1; j <= 9; j++) {  
box = eval("" + j);   
 = !;  
   }  
}  
//  End -->  
</script>  
</head>  
<body>  
<form name=checkboxform>  
<input type=checkbox name=C1>C1<br>  
<input type=checkbox name=C2>C2<br>  
<input type=checkbox name=C3>C3<br>  
<input type=checkbox name=C4>C4<br>  
<input type=checkbox name=C5>C5<br>  
<input type=checkbox name=C6>C6<br>  
<input type=checkbox name=C7>C7<br>  
<input type=checkbox name=C8>C8<br>  
<input type=checkbox name=C9>C9<br>  
<br>  
<input type=button value="Select all" onClick="checkAll()"><br>
<input type=button value="Cancel" onClick="uncheckAll()"><br>
<input type=button value="Anti-select" onClick="switchAll()"><br>
</form> 