casper.waitForSelector(x('//button[@class="addToShopcart"]'),
    function success(indexNumber) {
        casper.echo(stripLineBreaksTrim(casper.fetchText(x('//select[@id="artikel"]//option['
+ indexNumber + ']'))));
    },
    function fail() {});

casper.echo(stripLineBreaksTrim(casper.evaluate(function(){
    return document.querySelector('#artikel').selectedOptions[0].innerHTML;
})));