js封装获取昨天、今天和明天的日期的方法

    // 获取今天
    var day = new Date();
    // 减去一天的毫秒数
    day.setTime(day.getTime() - 24 * 60 * 60 * 1000);
    // 写成yyyy-mm-dd的格式
    var yesterday = day.getFullYear() + "-" + (day.getMonth() + 1) + "-" + day.getDate();
    console.log(yesterday); //昨天的日期  2022-8-30

    // 这里重新又获取今天的事件而不直接用上边的day是因为 上边的day已经变成了昨天的日期
    console.log(day); // Tue Aug 30 2022 20:54:42 GMT+0800 (GMT+08:00)
    var day = new Date();
    console.log(day); // Wed Aug 31 2022 20:54:42 GMT+0800 (GMT+08:00)
    day.setTime(day.getTime());
    var today = day.getFullYear() + "-" + (day.getMonth() + 1) + "-" + day.getDate();
    console.log(today); //今天的日期 2022-8-31

    var day = new Date();
    // 加上一天的毫秒数
    day.setTime(day.getTime() + 24 * 60 * 60 * 1000);
    var tomorrow = day.getFullYear() + "-" + (day.getMonth() + 1) + "-" + day.getDate();
    console.log(tomorrow); // 明天的日期 2022-9-1

进行封装一下：

    function getDay(num, str) {
        var today = new Date();
        var nowTime = today.getTime();
        // 毫秒数
        var ms = 24 * 3600 * 1000 * num;
        today.setTime(parseInt(nowTime + ms));
        var year = today.getFullYear();
        var month = (today.getMonth() + 1).toString();
        var day = today.getDate().toString();
        return year + str + month + str + day;
    }
    // -1表示前一天 1表示明天
    var yesterday = getDay(-1, '-') // 2022-8-30
    var today = getDay(0, "-") // 2022-8-31
    var tomorrow = getDay(1, "-") // 2022-9-1