How to calculate number of checkboxs'Id in a table via Javascript

I wanna get the total number of the checkbox in a html.

request: (1) By Javascript (2) all my checkbox id is "id=idCheckBox", (3) each checkbox name is reserved for back-end using. not for javascript. (4) The naming for each checkbox's name is like checkbox_1, checkbox_2,... where the number indicate the serial number of a checkbox.

The Table Html

<table class="form_table" border="0" cellpadding="0" width="750px" id="idRoutineListTable">   
<tr>
   <td style="align:center;" class="routineListCell">
   <input type='checkbox' name='checkbox_1' id='idCheckBox'></input>
   <!-- It may many checkbox here.-->
   </td>
</tr>
</table>    

My JS code, the function is to check any checkbox is selected before deletion. if no checkbox is selected, it pops up warning.

function beforeDelete()  /*{{{*/ 
{
    var checked=0;
    var checkboxAll=document.all["idCheckBox"];
    //the开发者_运维知识库 error is here, when there is only one checkbox, I cannot get length value, 
    //coz checkboxAll is not recognized as an array. However, if there are more than  
    //two checkboxes, the function works.
    alert (checkboxAll.length);    
    for(var i=0;i<checkboxAll.length;i++) {
        if (checkboxAll[i].checked==true) {
            checked++;
        }
    }
    if(checked==0) {
        alert('Please select the item you will delete');
        return false;
    } 
}  /*}}}*

The problem has indicate in the above code. Any idea to solve this?

here is a full working sample using jQuery:

<script src="../../Scripts/jquery-1.5.1.js" type="text/javascript"></script>
<script>
    function beforeDelete() {
        if ($("input:checked").length == 0) {
            alert('Please select the item you will delete');
            return false;
        }
        return true;
    }
</script>


<form onsubmit="return beforeDelete()">
    <table class="form_table" border="0" cellpadding="0" width="750px" id="idRoutineListTable">   
    <tr>
       <td style="align:center;" class="routineListCell">
       <input type='checkbox' name='checkbox_1' id='idCheckBox'></input>
       <input type='checkbox' name='checkbox_2' id='idCheckBox'></input>
       <input type='checkbox' name='checkbox_3' id='idCheckBox'></input>
       <!-- It may many checkbox here.-->
       </td>
    </tr>
    </table>   
    <input type="submit" />
</form>

Try this:

function beforeDelete()  {
    var checkboxAll=document.getElementsByTagName("input");   
    for(var i=0;i<checkboxAll.length;i++) {
        var input = checkboxAll[i];
        if (input.type == "checkbox" && input.checked==true) {
            return true;
        }
    }

    alert('Please select the item you will delete');
    return false;   
}

The first decision: You may use checkboxAll.length as a condition to check if there is only one checkbox in your markup.

if(checkboxAll.length == undefined)

If not, you may use your code with loop, if it is only one checkbox - check only one.

The second decision: To use getElementsByTag that will return you an array. In this case you need to filter this array with the given id

Demo for both decisions here