Simple queue implementation

queue.js

// For Quokka, as localStorage is not available in Node.js
const localStorage = {
    getItem(name) {
        return localStorage[name];
    },
    setItem(name, value) {
        localStorage[name] = value;
    },
};

const queue = {
    items: [],
    fn: null,
    namespace: '__queue__',

    // Public

    start(fn) {
        if (this.fn) {
            throw new Error('Queue has already started');
        }

        if (typeof fn !== 'function') {
            throw new Error(`Invalid type for "fn" argument, got "${typeof fn}"`);
        }

        this.fn = fn;
        this.next();
    },
    push(item) {
        const isFirst = this.items.push(item) === 1;
        this.save();

        if (isFirst && this.fn) {
            this.next();
        }
    },
    import() {
        try {
            this.items = [
                ...JSON.parse(localStorage.getItem(this.namespace)),
                ...this.items,
            ];
        } catch (ex) {
            // Ignore
        }
    },
    reset() {
        this.items.length = 0;
    },
    save() {
        localStorage.setItem(this.namespace, JSON.stringify(this.items));
    },

    // Internal
    next(dequeue = false) {            
        if (dequeue) {
            this.items.shift();
            this.save();
        }
        
        if (this.items.length > 0) {
            const item = this.items[0];
            this.fn(item, this.next.bind(this, true), this.cancel.bind(this));
        }
    },
    cancel() {
        console.error(`An error occurred with the queue item "${this.items[0]}". The queue has stopped`);
        this.reset();
    },
};

queue.import();
queue.push(1);
queue.push(2);
queue.push(3);
queue.start(request);
queue.push(4);
queue.push(5);

function request(num, next, cancel) {
    const delay = num * 200;
    
    setTimeout(() => {
        console.log('Num:', num, 'Delay:', delay);

        if (Math.random() < 0.5) {
            next();
        } else {
            cancel();
            console.log(localStorage.__queue__);
        }
    }, delay);
}