How to checked checkbox if boolean value is true?

Question

I'm working on jsp application and I have a form that has a checkbox, I retrieve data from my database which has a bit field named "principal", I can get the value of this field which is a boolean but I can't checked or unchecked the checkbox depending on the value of "principal".

Here's my JSP code:

<tr>
 <td>Principal:</td>
  <td colspan="2">
   <input type="checkbox" id="a_principal" name="a_principal" value="<%=directorio.isPrincipal()%>"/>
  </td>
</tr>

Javascript code:

$(function (){
    if('#a_principal' == true){
         $("input:checkbox").attr('checked', true);
    }else{
        $("input:checkbox").attr('checked', false);
    }

});

Thanks in advanced.

Answer 1

Using prop to set checked property and get your if condition right. attr is not guaranteed to work against boolean properties of element and prop is. See the difference here . Also the condition '#a_principal' == true is always true.

$("input:checkbox").prop('checked', $('#a_principal').length); 
// i dont know if you meant $('#a_principal').prop('checked') then
$("input:checkbox").prop('checked', $('#a_principal').prop('checked'));  
//but here :checkbx generic selector will select a_principal as well, so be specific 

Providing your complete html will help solving your issue in a better way however try this:

   var $principal = $('#a_principal');
   $("input:checkbox").not($principal).prop('checked', $principal.prop('checked'));  

Answer 2

try with .prop instead of .attr()

$(function (){
    if($('#a_principal').val()== "true"){           
         $("input:checkbox").prop('checked',true);
    }else{
        $("input:checkbox").prop('checked', false);
    }
});

Js Fiddle Demo