factory.js

app.factory('mathFactory',function(){
	var factory = {};
  
  factory.mod = function(a,b){
  	return a % b;
  }
  
  return factory;
});

app.service('calcService',function(mathFactory){
  this.isEven = function(a){
  	return mathFactory.mod(a,2) === 0;
  }
});