Lottery is not working

I tried to make a small lottery picking 6 random numbers out of 49 wich are all different. This is what I came up with but something isn`t working. Can you tell me what is wrong and correct the code? Thanks

function getNumbers(){
    var numbers = [];
    var randomnumber;

    while(numbers.length < 6){
            randomnumber = Math.ceil(Math.random()*49)
            if(arr.indexOf(randomnumber) > -1) continue;
            numbers[numbers.length] = randomnumber;
    }

    numbers.sort(sortNumber);

    document.getElementById("Ausgabe").innerHTML = numbers;
}



function sortNumber(a,b) {
        return a - b;
    }