JS localStorage basic caching for a day

cache_for_a_day.js

// Usage: cache_for_a_day('data_id', <data>);
// If you only provide an ID, it gets
// If you provide both, it checks the date and returns cached data if it's been cached less than a day. Otherwise it sets the new data

function cache_for_a_day(id, data) {
	var new_data = {};
	var old_data = JSON.parse(localStorage.getItem(id));
	
	if (old_data) {
	    var cache_date = new Date(old_data.cache_date);
	    var today = new Date();
	
	    if (cache_date.getTime() > today.getTime()) {
	        // using cache
	        return old_data.data;
	    }
	}

	if (data) {
	    // saving a cache
	    var date = new Date();
	    date.setDate(date.getDate() + 1);
	    new_data.cache_date = date;
	    new_data.data = data;
	
	    localStorage.setItem(id, JSON.stringify(new_data));
	    return false;
	}
}