Check/UnCheck All

var checked = false;

function check(field) {
     if (!checked) { // if checkboxes are not checked then check them
          for (i = 0; i < field.length; i++) { // loop through the array of checkboxes & check them
               field[i].checked = true;
          }
          checked = true;
          return "Uncheck All";  // change the button label
     }
     else {
          for (i = 0; i < field.length; i++) { // loop through the array of checkboxes & uncheck them
               field[i].checked = false;
          }
          checked = false;
          return "Check All";  // change the button label
     }
}

</SCRIPT>

<FORM >
     <INPUT TYPE="checkbox" NAME="lang" VALUE="1">Java
     <INPUT TYPE="checkbox" NAME="lang" VALUE="2">JavaScript
     <INPUT TYPE="checkbox" NAME="lang" VALUE="3">ASP
     <INPUT TYPE="checkbox" NAME="lang" VALUE="4">HTML
     <INPUT TYPE="checkbox" NAME="lang" VALUE="5">SQL
     <INPUT TYPE="button" VALUE="Check All"
       onClick="this.value=check(this.form.lang)">
</FORM>