What are standard ways to show that your functions are connected to a certain JSON data structure?

I've a JSON file with a structure that is not yet set; it may grow complex. I want to keep track of what the functions think the data structure is.

What are standard/smart ways to show that your functions is connected to a certain data structure?

Right now, I'm using a _comment in the json file to keep a version number, and then keeping that version name as a comment in each function that uses it. Full example below.

travel.json

{
  "_comment" : "version 1.0"
, "name" : "Tom Sawyer"
, "travel" : [{
   "id" : "1"
,  "location" : "San Francisco"
  }, {
   "id" : "2"
,  "location" : "London"
  }]
}

Two functions to parse: travel.json

fs = require('fs');

function get_json() {

    var file = __dirname + '/travel.json';
    data = fs.readFileSync(file, 'utf8');
    var json_obj = JSON.parse(data);
    return(json_obj);

 };

function get_location(json_obj) {
    // "version 1.0"

    var new_obj = {};
    json_obj.content.forEach(function(item) { 
        new_obj[item.id] = item.location;
    });
    return ( new_obj );

};

// Run 
console.log('Locations: ', get_location( get_json() ));

Thanks.