stack-with-max.js

class Stack {
    constructor() {
        this.array = []
    }

    push(value) {
        this.array.push(value)
    }

    pop() {
        return this.array.pop()
    }

    max() {
        if (!this.array.length) {
            return
        }
        let first = this.array.pop()
        let temp = [first]
        let max = first
        while (this.array.length) {
            let current = this.array.pop()
            temp.push(current)
            max = Math.max(max, current)
        }
        while (temp.length) {
            this.array.push(temp.pop())
        }
        return max
    }
}