Balanced Brackets Problem - Hackerrank

balanced_brackets.js

function Node(data) {
    this.data = data;
    this.next = null;
}
function Stack() {
    this.top = null;
}
Stack.prototype.push = function(data){
    let node = new Node(data);
    if(this.top == null){
      this.top = node; 
      return;  
    } 
    node.next = this.top;
    this.top = node;
    return;
}
Stack.prototype.pop = function(){
    if(this.top == null) return;
    let data = this.top.data;
    this.top = this.top.next;
    return data;
}

Stack.prototype.empty = function(){
    return this.top == null;
}


function isBalanced(s) {
    let pairs = {"}": "{", "]": "[", ")": "("};
    let res = new Stack()
    for(let i=0; i <= s.length -1; i++){
        if(pairs[(s[i])]){
            let popped = res.pop();
            if (pairs[s[i]] != popped) return "NO"; 
        }else{
            res.push(s[i]);
        }
    }
    return (res.empty()) ? "YES" : "NO"; 
}