About JavaScript control check box Select all, you must choose one, control the number of code

<script type= "Text/javascript Tutorial" >

function Check ()
{
var F=document.getelementbyid ("Form1");
var obj=document.getelementsbyname ("User");
for (Var i=0;i<obj.length;i++)
{
if (obj[i].checked==true)
{
var flag= "OK";
Break
}
}
if (flag!= "OK")
{
Alert ("Please select Recipient!") ");
return false;
}
Else
{
return true;
}
}

</script>

Html:

<input type= "checkbox" name= "User" value= "1"/>
<input type= "checkbox" name= "User" value= "2"/>
<input type= "Submit" Name= "Submit1" onclick= "return Check ()" value= "Send"/>

<script language=javascript Tutorials >    
///First method     

function Selectall1 ()
{
var a = document.getElementsByTagName ("input");
if (a[0].checked==true) {
for (var i=0 i<a.length; i++) <= "span=" >
if (A[i].type = = "checkbox") a[i].checked = false;
}
Else
{
for (var i=0 i<a.length; i++) <= "span=" >
if (A[i].type = = "checkbox") a[i].checked = true;
}
}  

The second method

function Selectall2 () {
var tform = document.forms[' Form1 '];
for (Var i=0;i<tform.length;i++) <= "span=" >
{
var e = tform.elements[i];
if (E.type = "checkbox")
e.checked =!e.checked;
}
}

The third method, combined with both of these methods

function Selectall3 ()
{
var a = document.getElementsByTagName ("input");
for (var i=0 i<a.length; i++) <= "span=" >
if (A[i].type = = "checkbox") a[i].checked =!a[i].checked;
}    

Fourth method

function Selectall4 (ID) {//ID Distinguished
var tform=document.forms[' Form1 '];
for (Var i=0;i<tform.length;i++) {<= "" span= "" >
var e=tform.elements[i];
if (e.type== "checkbox" && e.>}
}    

Fifth method

function SelectAll (theform,thename) {//theform specified form,thename is the Name property of the checkbox
var tform=document.forms[theform];
document.getElementById ("Thewen"). Value= ' reverse election ';
for (Var i=0;i<tform.length;i++) {<= "" span= "" >
var e=tform.elements[i];
if (e.type== ' checkbox ' && e.>}
}    

</script>

Controlling the number of checkbox

<script language= "JavaScript" >
function cc ()
{
var Oc=document.form1.sitem;
var t=0;

if (OC)
{
for (Var i=0;i<oc.length;i++) {
if (OC (i). Checked) t++
}
}

if (t>7 && t<9) alert ("You can only choose 7, but you chose" + t + "");
}

</script>

<body>

<script language= "JavaScript" >

</script>

<form name= "Form1" Id= "Form1" action= "nextpage.htm" >
Please select up to 7 items:
<p>
<input type= "checkbox" Value= "CRC" Name= "Sitem" > Www.111cn.net <br/>
<input type= "checkbox" value= "Northsnow" name= "Sitem" id= "CheckBox1" > Northern Snow <br/>
<input type= "checkbox" value= "Csdn" name= "Sitem" id= "CheckBox2" > China's largest developer network <br/>
<input type= "checkbox" Value= "a" name= "Sitem" id= "Checkbox3" > Fly <br/>
<input type= "checkbox" value= "B" name= "Sitem" id= "checkbox4" > Snow <br/>
<input type= "checkbox" Value= "C" name= "Sitem" id= "checkbox5" > Lian <br/>
<input type= "checkbox" value= "D" name= "Sitem" id= "checkbox6" > Day <br/>
<input type= "checkbox" Value= "E" name= "Sitem" id= "checkbox7" > Shot <br/>
<input type= "checkbox" value= "F" name= "Sitem" id= "checkbox8" > White <br/>
<input type= "checkbox" value= "G" name= "Sitem" id= "checkbox9" > Deer <br/>
<input type= "button" name= "ss" value= "OK" onclick= "cc ();" >
</form>
</body>