typescript stack

collection.ts

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

class Stack implements Collection {
  top: any

  constructor() {
    this.top = null;
  }

  push(value: any) {
    this.top = {
      value: value,
      next: this.top
    };
  }

  pop() {
    var value = this.top.value;
    this.top = this.top.next;
    return value;
  }

  peek() {
    return this.top.value;
  }

  isEmpty() {
    return this.top === null;
  }
}