function Queue () { 
    collection = [];
    this.print = function() {
        console.log(collection);
    };
    // Only change code below this line
    this.enqueue=function(arr){
        collection.push(arr);
    };
    this.dequeue=function(){
        return collection.shift();
    };
    this.front=function(){
        return collection[0];
    };
    this.size=function(){
        return collection.length;
    };
    this.isEmpty=function(){
    };
    // Only change code above this line
}