Stack with Array.js

class Stack{

	constructor(length){
		this.data = new Array(length);
		this.pointer = 0;
	}
	
	push(value){
		if(this.pointer === this.data.length){
			throw "Overflow"
		}
		
		this.data[this.pointer] = value;
		this.pointer++;
	}
	
	pop(){
		var value = this.data[this.pointer - 1];
		this.pointer--;
		return value;
	}
	
	peek(){
		if(this.data.length > 0)
			return this.data[this.pointer - 1];
		else 
			return null;
	}
	
}

var stack = new Stack(5);
stack.push(1);
stack.push(2);
stack.push(3);
stack.push(4);
stack.push(5);
console.log(stack.peek());
stack.pop();
console.log(stack.peek());