Stack Implementation in JavaScript

stack.js

class Stack {
    constructor(list) {
        this.list = {}
        this.count = 0
    }

    push(value) {
        this.list[this.count] = value
        this.count++
    }

    pop() {
        if ( this.count === 0) { return null }
        this.count--
        const item = this.list[this.count]
        delete this.list[this.count]
        return item
    }

    peek() {
        return this.list[this.count - 1]
    }

    size() {
        return this.count
    }

    empty() {
        return this.count === 0
    }

    swap() {
        const i = this.count - 1
        let first = this.list[i]
        let second = this.list[i - 1]
        console.log(first, second)
        this.list[i] = second
        this.list[i - 1] = first
    }

}