📬栈的JavaScript实现

更详尽参看：
4️⃣ 栈

利用数组实现

class StackArray {
    constructor() {
        this.items = []
    }
    push(elem) {
        this.items.push(elem)
    }
    pop() {
        if (this.isEmpty()) {
            return undefined
        }
        return this.items.pop()
    }
    isEmpty() {
        return this.items.length === 0
    }
    peek() {
        if (this.isEmpty()) {
            return undefined
        }
        return this.items[this.items.length - 1]
    }
    size() {
        return this.items.length
    }
    clear() {
        this.items = []
    }
    toString() {
        let objString = ''
        return this.items.reduce((prev,cur,index)=> {
            if (index === this.items.length - 1) {
                return prev+cur
            }
            return prev+cur+','
        },'')
    }
}
let s = new StackArray()
s.push(1)
s.push(2)
s.push('1111')
console.log(s)
console.log(s.toString())
s.pop()
console.log(s.size())
console.log(s.peek())
s.clear()
console.log(s)
console.log(s.size())
console.log(s.peek())
// 输出
// StackArray { items: [ 1, 2, '1111' ] }
// 1,2,1111
// 2
// 2
// StackArray { items: [] }
// 0
// undefined

利用对象实现

class Stack {
    constructor() {
        this.count = 0
        this.items = {}
    }
    push(elem) {
        this.items[this.count] = elem
        this.count++
    }
    pop() {
        if (this.isEmpty()) {
            return undefined
        }
        this.count--
        const result = this.items[this.count]
        delete this.items[this.count]
        return result
    }
    peek() {
        if (this.isEmpty()) {
            return undefined
        }
        return this.items[this.count - 1]
    }
    isEmpty() {
        return this.count === 0
    }
    size() {
        return this.count
    }
    clear() {
        this.items = {}
        this.count = 0
    }
    toString() {
        if (this.isEmpty()) {
            return ''
        }
        let objString = `${this.items[0]}`
        for(let i=1;i<this.count;i++){
            objString += `,${this.items[i]}`
        }
        return objString
    }
}
let s = new Stack()
s.push(1)
s.push(2)
s.push('1111')
console.log(s)
console.log(s.toString())
s.pop()
console.log(s.size())
console.log(s.peek())
s.clear()
console.log(s)
console.log(s.size())
console.log(s.peek())
// 输出
// Stack { count: 3, items: { '0': 1, '1': 2, '2': '1111' } }
// 1,2,1111
// 2
// 2
// Stack { count: 0, items: {} }
// 0
// undefined