set input checked by default not displaying

I have an issue about the initialization of a checkbox. I have set it by default in the HTML file like this (with attribute checked) :

<label><input type="checkbox" value="" checked>User vs Computer</label>

Here's the full HTML code

It works fine on jsfiddle (when I reload the page, non matter the checked input, I get only the first input to be checked).

But my problem is that I can't get it work in local : it does nothing when I reload the page, the checked/unchecked inputs stay the same.

Where could this error come from ?

Thanks