Edit in JSFiddle

CalcModule = (function($){
                       var pub = {};
                       var INVALID = 'invalid input';
                       pub.add = function(a,b){
                                     if($.isNumeric(a) && $.isNumeric(b)){
                                         return a+b;
                                     }
                                     else{
                                         return INVALID;
                                     }
                       };
                       
                       pub.sub = function(a,b){
                                     if($.isNumeric(a) && $.isNumeric(b)){
                                          return a-b;
                                     }
                                     else{
                                         return INVALID;
                                     }
                       };
                       
                       return pub;
}(jQuery)); //passed 'jQuery' global variable into local parameter '$'

alert CalcModule.add('abc',2): 
<button onclick="alert(CalcModule.add('abc',2))">'abc' + 2</button>
<br>
alert CalcModule.add(5,2): 
<button onclick="alert(CalcModule.sub(5,2))">5 - 2</button>