_JavaScript_queue

queue.js

class Queue {
    constructor() {
        this.list = [];
        this.first = null;
    }

    enqueue(v) {
        if (this.first === null) {
            this.first = v;
        }
        this.list.push(v);
    }

    depueue() {
        if (this.first === null) {
            return null;
        }

        let [remove, ...rest] = this.list;
        this.list = rest;

        if (this.list.length === 0) {
            this.first = null;
        }
        else {
            this.first = this.list[0];
        }
        return remove;
    }

    peek() {
        return this.first;
    }
}

const q = new Queue();
q.enqueue(1)
q.enqueue(2)
q.enqueue(3)

console.log(q.peek()); // 1
console.log(q.depueue()); // 1
console.log(q.peek()); // 2
console.log(q.depueue()); // 2
console.log(q.peek()); // 3
console.log(q.depueue()); // 3
console.log(q.peek()); // null