foo.js

var month = require('C:/Users/Asus/Desktop/mod.js');

console.log(month.toNum('January'));

mod.js

function monthz () {
    var months = ["January", "February", "March", "April"];

    exports.toNum = function(name) {
        return months.indexOf(name) + 1;
    }

    exports.toMon = function(num) {
        return months[num];

    }
}
monthz();