In Mustache, How to get the index of the current Section

This is how I do it in JavaScript:

var idx = 0;

var data = { 
   "names": [ 
       {"name":"John"}, 
       {"name":"Mary"} 
    ],
    "idx": function() {
        return idx++;
    }
};

var html = Mustache.render(template, data);

Your template:

{{#names}}
    {{name}} is {{idx}}
{{/names}}