You have jQuery tagged in your question, so I'm going to provide a jQuery answer:
You'd use jQuery's on() method to delegate the event to a non-dynamic ancestor of your checkbox:
$('elem').on('change', 'input[type="checkbox"]', function() {
...
});
Where elem is a non-dynamic ancestor of your checkbox.
In your JSFiddle your checkbox isn't dynamic, but assuming it was, the closest non-dynamic ancestor of it would be the document's body. Therefore, we can use:
$('body').on('change', 'input[type="checkbox"]', function() {
testing('hello', '1');
});
JSFiddle demo.
You may want to extend this by passing in "hello" and "1" as data-* attributes:
<input type="checkbox" name="test" data-newvalue="hello" data-spanid="1" />
<input type="checkbox" name="test" data-newvalue="second" data-spanid="2" />
Here I've created two checkboxes with our two data-* attributes. In our jQuery method we can pull these values and pass them into our testing() function using jQuery's data() method:
$('body').on('change', 'input[type="checkbox"]', function() {
testing($(this).data('newvalue'), $(this).data('spanid'));
});
JSFiddle demo.
We can then modify our testing() function to also use jQuery:
function testing(newValue, spanID) {
$('#'+spanID).text(newValue);
}
This pulls our spanID (e.g. "1") and places it within an ID selector $('#1'), then modifies the text using jQuery's text() method. If you wanted to modify the HTML instead, jQuery also has a html() method for this purpose.
Final JSFiddle demo.