Typescript Stack

gistfile1.txt

interface Collection {
  pop(): number;
  push(value: number): void;
  peek(): number;
  isEmpty(): boolean;
}

class Stack implements Collection {
  value: number;
  pointer: any;
  pop() {
    var next = this.pointer;
    var result = null;
    if (this.pointer === null) {
      result = this.value;
      this.value = null;
      return result;
    } else {
      result = this.pointer.value;
      this.pointer = this.pointer.pointer;
      return result;
    }

  }
  push(value: number) {
    var previousPointer = this.pointer;
    var nextNode = new Stack(value);
    if (!this.pointer) {
      this.pointer = nextNode;
    } else {
      this.pointer = nextNode;
      nextNode.pointer = previousPointer;
    }
  }
  peek() {
    var next = this.pointer;
    if (this.pointer === null) {
      return this.value;
    } else {
      return this.pointer.value;
    }
  }
  isEmpty() {
    if (this.pointer === null) {
      return true;
    } else {
      return false;
    }
  }
  constructor(value: number) {
    this.value = value;
    this.pointer = null;
  }
}

var stack1 = new Stack(1);
stack1.push(3);
stack1.push(5);
stack1.pop();
console.log(stack1.isEmpty());
stack1.pop();
console.log(stack1.peek());
stack1.pop();
console.log(stack1.isEmpty());