# JavaScript Exercises: Nth element from the top of the stack

## JavaScript Stack: Exercise-16 with Solution

Write a JavaScript program to get the nth element from the top of the stack.

Sample Solution:

JavaScript Code:

``````class Stack {
constructor() {
this.items = [];
}
push(element) {
this.items.push(element);
}
pop() {
if (this.isEmpty()) {
return "Underflow";
}
return this.items.pop();
}
peek() {
return this.items[this.items.length - 1];
}
isEmpty() {
return this.items.length === 0;
}
size() {
return this.items.length;
}
getNthFromTop(n) {
if (this.items.length < n) {
return "Index out of range";
}
return this.items[this.items.length - n];
}
displayStack(stack) {
console.log("Stack elements are:");
let str = "";
for (let i = 0; i < stack.items.length; i++)
str += stack.items[i] + " ";
return str.trim();
}
}
let stack = new Stack();
stack.push(100);
stack.push(200);
stack.push(300);
stack.push(400);
stack.push(500);
stack.push(600);
stack.push(700);
console.log(stack.displayStack(stack));
n = 2;
console.log("nth element from the top of the stack where n = "+n);
console.log(stack.getNthFromTop(n));
n = 5;
console.log("nth element from the top of the stack where n = "+n);
console.log(stack.getNthFromTop(n));
n = 7;
console.log("nth element from the top of the stack where n = "+n);
console.log(stack.getNthFromTop(n));
```
```

Sample Output:

```Stack elements are:
100 200 300 400 500 600 700
nth element from the top of the stack where n = 2
600
nth element from the top of the stack where n = 5
300
nth element from the top of the stack where n = 7
100
```

Flowchart:

Live Demo:

See the Pen javascript-stack-exercise-16 by w3resource (@w3resource) on CodePen.

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## JavaScript: Tips of the Day

Creates an array of elements, ungrouping the elements in an array produced by zip and applying the provided function

Example:

```const tips_unzip = (arr, fn) =>
arr
.reduce(
(acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc),
Array.from({
length: Math.max(...arr.map(x => x.length))
}).map(x => [])
)
.map(val => fn(...val));

console.log(tips_unzip([[2, 15, 200], [3, 25, 300]], (...args) => args.reduce((acc, v) => acc + v, 0)));
```

Output:

```[5, 40, 500]
```