How to write a helper in javascript for Multiplying arrays and strings together?

Question

This is just a thought experiment in me trying to learn javascript and a idea called duck typing.

function calc(a,b,c) {
    return (a+b)*c;   
}

var example1 = calc(1,2,3);
var example2 = calc([1,1,3],[2,2,3],3);
var example3 = calc ('ape ', 'and cat, ', 3)
console.log(example1, example2, example3);

How can I make the return values appear like so:

9
[1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6]
ape and cat, ape and cat, ape and cat,

Currently they will print out as:

9
NaN 
NaN

are there helpers in lo-dash?

Here's the sample code: http://repl.it/4zp/2

Answer 1

This should work with strings, numbers and arrays. Additionally, I did toy around with the idea of converting arrays to string and back again if we want to implicitly use the + operator in a similar way to strings.

function calc(a, b, c) {
    var combine, total, 
        isArray = a instanceof Array && b instanceof Array,
        i;

    combine = total = isArray ? a.concat(b) : a + b;

    for (i = 1; i < c; i++) {
        total = isArray ? total.concat(combine) : total += combine;
    }

    return total;
}

Answer 2

it is just to show you what it suppose to do and what duck typing means.but the implementation should be done by you.it may be something like this:

function calc(a,b,c) {
     var ret=[];
 if(a.constructor === Array && b.constructor === Array){
     for(i=0;i<c;i++){
       ret=ret.concat(a.concat(b));
   }
       return ret;
     }

 if(typeof a == 'string' && typeof b == 'string'){
     var str='';
     for(i=0;i<c;i++){
         str=str+a+b;
     }
     return str;
 }

        return (a+b)*c;   
    }

    var example1 = calc(1,2,3);
    console.log(example1)
    var example2 = calc([1,1,3],[2,2,3],3);
    console.log(example2)
    var example3 = calc ('apples ', 'and oranges, ', 3)
    console.log(example3)

NOTE: you can add many more conditions to it.