Unable to sort arrays in Javascript

var arr1 = ['a1','a2','a3,' ,'b1', 'b2' , 'c1' , 'c2'];
var arr2 = [];
var userInput = 7;
do{
    for (var i =0; i < arr1.length; i++)
        {
            if (arr2.indexOf(arr1[i]) == -1 ))
            {
                    arr2.push(arr1[i]);

                if (arr2.length == userInput)
                    {
                        break;
                    }

            }
}
}while (arr2.length == userInput);
console.log(arr2)
//output = ["a1", "a2", "a3,", "b1", "b2", "c1", "c2"]
//expected output = ["a1", "b1", "c1,", "a2", "b2", "c2", "a3"]