Получить возраст, используя момент

var a = moment();
var b = moment('{dem_pat_birthyear}', 'YYYY');  
var diff = a.diff(b, 'years'); // calculates patient's age in years
diff; // this prints out the age
//In this calculation {dem_pat_birthyear} 
//needs to be replaced with your variable name for birth year. 
Vivacious Vendace