SOURCE

class Queue{
    constructor(){
        this.count = 0;
        this.lowestCount = 0;
        this.items = {}
    }

    enqueue(ele){ //向队尾添加一个或多个项
        this.items[this.count] = ele
        this.count++
    }

    dequeue(){  //移除队列第一项
        if(this.isEmpty()){
            return undefined
        }
        const result = this.items[this.lowestCount]
        delete this.items[this.lowestCount]
        this.lowestCount++
        return result
    }
    peek(){ //返回队列中第一个元素
        if(this.isEmpty()){
            return undefined
        }
        return this.items[this.lowestCount]
    }
    isEmpty(){
        return this.count - this.lowestCount === 0
    }
    size(){
        return this.count - this.lowestCount
    }
    clear(){
        this.count = 0;
        this.lowestCount = 0;
        this.items = {}
    }
    toString(){
        if(this.isEmpty){
            return ""
        }
        let objString = `${this.items[this.lowestCount]}`
        for(let i = this.lowestCount+1; i<this.count; i++){
            objString = `${objString}, ${this.items[i]}`
        }
        return objString 
        
    }
}

let myQueue = new Queue()
myQueue.enqueue(12)
myQueue.enqueue(45)
console.log(myQueue.isEmpty())
console.log(myQueue.toString())
console.log(myQueue.dequeue())