form validation

get users to check box before submitting

[HelenDev]

This is kind of a continuation of a question I asked a while back. It has taken me so long to get around to doing this that the thread has expired!

Anyway...

Fotiman very kindly posted some code to do this...

<script type="text/javascript"> 
function isChecked( checkboxId ) 
{ 
 var cbox = document.getElementById(checkboxId); 
 if(!cbox ) return false; 
 if( cbox.checked ) 
 { 
 return true; 
 } 
 return false; 
} 
</script> 
<form onsubmit="return isChecked(myCheckBox)"> 
<input type="checkbox" id="myCheckBox" name="myCheckBox"> 
<input type="submit" name="submit" value="Submit"> 
</form> 

But my knowledge of javascript is a bit basic, so how do I use the returned value of the function to create an alert?

Also, including the onsubmit part seems to stop my form from actually submitting?

[Bernard Marx]

This is a basic version. I removed the bit that checks for the existence of the checkbox itself. We might as well assume it exists (although we could check for DOM 1 support, and return true if not).

<script type="text/javascript"> 
function isChecked( checkboxId ) 
{ 
  var cbox = document.getElementById(checkboxId);
  var valid = cbox.checked; /* boolean value */
  if(!valid)
    alert("Oi! That box ain't checked");
  return valid;  
} 
</script> 
<form onsubmit="return isChecked(myCheckBox)"> 
<input type="checkbox" id="myCheckBox" name="myCheckBox"> 
<input type="submit" name="submit" value="Submit"> 
</form>