Function of getting a random property of object stop working properly after the reassigning

My function to get a random property of object at some point start create a new empty arrays (my properties contain arrays); here's the snippet of my code:

var randomProperty = function (obj) {
    var keys = Object.keys(obj)
    return obj[keys[ keys.length * Math.random() << 0]];
};//function to get a random property


var new_arr=randomProperty(questions_test);//just the random property from object(property consists of arrays)
var duplicate=new_arr.slice(0);//copy of array,i need it to restore array when it's empty
$('.primary,.tertiary').click(function() {
if(new_arr.length===0){//restore the array
    new_arr=duplicate.slice(0);
}
var get_question = new_arr[Math.floor(Math.random()*new_arr.length)];
var indexOfQuestion=new_arr.indexOf(get_question);
if(new_arr.length>0){ //trying to avoid repeating of questions 
        new_arr.splice(indexOfQuestion,1);  
}



    $('.secondary').click(function(){
new_arr=randomProperty(questions_test);
duplicate=new_arr.slice(0);
console.log("The button 'extend' is clicked");
});

I can give a jsfiddle link http://ift.tt/1TVT3h1 ; it supposed to give you questions which will not repeat, if you interested in topic you can continue it , if you're not, you can change it.(just to make it clear)