function Stack() { 
    collection = [];
    this.print = function() {
console.log(collection);
    };
    // Only change code below this line
    this.push=function(arr){
        collection.push(arr);
    };
    this.pop=function(){
        return collection.pop();
    };
    this.peek=function(){
        return collection[collection.length - 1];
    };
    this.isEmpty=function(){
        return collection.length===0;
    };
    this.clear=function(){
        collection = [];
    };
    // Only change code above this line
}