javascript创建的基于canvas的倒计时计时器插件

使用方法

class Countdown {

    /**
     * @param {Date} dateTo
     */
    constructor(itemSelector, dateTo) {
        this.itemSelector = itemSelector;
        let $ = el => document.querySelector(el);
        this.dateSelectors = {
            d: $('.days').getContext('2d'),
            h: $('.hours').getContext('2d'),
            m: $('.minutes').getContext('2d'),
            s: $('.seconds').getContext('2d')
        };
        this.dateTo = dateTo;
        requestAnimationFrame(() => this.set());
    }

    /**
     * Main function
     */
    set() {

        let today = new Date();

        for (let selector in this.dateSelectors) {
            let s = this.dateSelectors[selector];
            this.clear(s);
            this.setTime(s, this.dateDiff(selector, today, this.dateTo));
        }
        requestAnimationFrame(() => this.set());
    }

    /**
     * Clear canvas
     * @param {canvas} ctx 
     */
    clear(ctx) { ctx.clearRect(0, 0, 60, 60); }

    setTime(ctx, until) {
        ctx.font = 'bold 2rem sans-serif';
        ctx.shadowColor = "#000";
        ctx.shadowOffsetX = 0;
        ctx.shadowOffsetY = 1;
        ctx.shadowBlur = 2;
        ctx.fillStyle = "#ccc";
        ctx.textAlign = "center";
        ctx.fillText(until, 25, 40);
    }

    /**
     * 
     * @param {String} datepart  enum {'m',  'd', 'h', 's'}
     * @param {Date} fromdate 
     * @param {Date} todate 
     */
    dateDiff(datepart, fromdate, todate) {
        datepart = datepart.toLowerCase();
        let diff = todate - fromdate;
        let divideBy = {
            d: 86400000,
            h: 3600000,
            m: 60000,
            s: 1000,
            ms: 1
        };

        let modulo = {
            d: 1,
            h: divideBy['d'],
            m: divideBy['h'],
            s: divideBy['m'],
            ms: divideBy['s']
        }

        return Math.floor(diff % modulo[datepart] / divideBy[datepart]);
    }

}

//set tomorrow date
new Countdown('.item-time', new Date(new Date().getTime() + 24 * 60 * 60 * 1000));