Discussion on: Implement a Stack with TypeScript

[Nik]

Hey Mark, very nice article. You demonstrate object hierarchy and genetics nicely. Just one question about the design, Why does the pop method on Stack<T> returns StackNode<T> instead of T. I push: string I should be pop: string. I push number I should pop number. What do you think?

[Mark Abeto]

Hi Nik, Good question. Yes, that's right you're pushing a value with type string or number but as you can see at right here.

push(val: T) {
    const node = new StackNode(val)
    // logic
}

the variable node holds a value object. If we have an example that looks like this.

const stack = new Stack()
stack.push('1')

that node variable will hold a value

StackNode { value: '1', next: null }

the value you're talking about is inside the object. We're using an object so that we can easily get the next value in the stack. If we use the pop method.

const popData  = stack.pop()

console.log(popData) 
// we will get the object StackNode { value: '1', next: null }.

[Nik]

I agree. Let me rephrase. The user of stack should be only aware of stack and the valueType it pushes or pops. It adds no value (in my opinion ) to give back stacknode of popped value.

So, it makes sense to use stacknode internally in stack to keep track of next value but don’t expose stacknode to the user of stack.

[Mark Abeto]

Awh ok. Sorry for the late reply. I think I understand what you're talking about. You want just the value correct not the object?. If that's what you want, you need two change two parts.

Stack Interface

interface Stack<T> {
  size: number
  top: StackNode<T> | null
  bottom: StackNode<T> | null
  push(val: T): number
  pop(): T | null
}

Stack pop implementation

pop(): T | null {
    if (this.size > 0) {
      const nodeToBeRemove = this.top as StackNode<T>
      this.top = nodeToBeRemove.next
      this.size -= 1
      nodeToBeRemove.next = null
      return nodeToBeRemove.value
    }
    return null
  }