Using for loop to populate array in document.getelementbyid

Question

i now facing a problem with using looping on my project. Currently i have a multiple checkbox which have their own unique id example :myCheckbox,myCheckBox1,myCheckBox2,....

I don't wish to hardcore the number behind the myCheckBox, so i try to use a for loop to get it done. Somehow i dono why my for loop does work, if i hardcode it like document.getelementbyid('mycheckbox1').checked==true then it work.

Anything i miss out in my code? Please guide me through as i'm still new to web programming. Thanks

Here is my code:

<script type='text/javascript'>

        function checkDisabled(yourSubmitButton){

          for(var i=0;i<10;i++){
              if(document.getElementById("myCheckBox"+i).checked==true){
                  yourSubmitButton.disabled = false;
                    return; 
              }
          } 


            // If we have made it here, disable it
            yourSubmitButton.disabled = true;

          };
          </script>

If getElementById can't find a particular element, it will return null. You cannot test .checked on a null object... so it will crash. You need to test for whether getElementById returns a valid object or not — freefaller
– freefaller, Commented Mar 26, 2015 at 8:47
The code is okay as far as it goes, although there's the question of myCheckbox vs myCheckbox0 (see my answer). We need to see your HTML. Also, you never need == true in conditions. And you will need to have 10 checkboxes for that code not to throw an error. — T.J. Crowder
– T.J. Crowder, Commented Mar 26, 2015 at 8:48
In general, your best option for figuring stuff like this out is to use the fully-featured debugger built into your browser. Press F12 or Ctrl+Shift+I or (on a Mac) Cmd+Shift+I or look in the menus, and you'll find a debugger with which you can step through code a statement at a time, look at the values of variables, see errors if there are errors that occur... There's no need to stumble around in the dark; your browser has one heck of a torch you can use. — T.J. Crowder
– T.J. Crowder, Commented Mar 26, 2015 at 8:50
Like the torch analogy @T.J - going to try and remember that one — freefaller
– freefaller, Commented Mar 26, 2015 at 8:54

T.J. Crowder · Accepted Answer · 2015-03-26 08:47:49Z

2

Stab in the dark: You've said in your question that your checkboxes are called myCheckbox, myCheckbox1, myCheckBox2, and such, but your loop is looking for myCheckbox0, not myCheckbox, on the first iteration, which would make it throw an exception when you try to read the checked property of null.

answered Mar 26, 2015 at 8:47

T.J. Crowder

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