function Queue () { 
    collection = [];
    this.print = function() {
        console.log(collection);
    };
    this.enqueue = function(element) {
        collection.push(element);
    };
    this.dequeue = function() {
        return collection.shift(); 
    };
    this.front = function() {
        return collection[0];
    };
    this.size = function() {
        return collection.length; 
    };
    this.isEmpty = function() {
        return (collection.length === 0); 
    };
}