Problem with addEventListener

Hi guys. I’m new to JavaScript.
I want to see the result of the below textbox as the user insert a number into the text box and it should change the currency when user select new currency.
Here’s my code:

window.addEventListener('load', fireUp, false);

function fireUp () {
    if ( document.getElementById('number') ) { //If brwoser support JavaScript
        var cost = document.getElementById('number').addEventListener('keydown', showResult, false);
        var currency = document.getElementById('currency').addEventListener('change', showCurrency, false);

        if ( cost && currency ) {
            var newCost = document.createTextNode(currency + cost);

function showResult (evt) {
    var insertedNumber =;
    return insertedNumber.value;

function showCurrency (evt) {
    var insertedCurrency =[];
    return insertedCurrency.text;

I don’t know why my functions don’t return the result when I call them by addEvenetListener.

Hamm, can you post your html as well