js計算兩個字符串日期相差天數

解決思路，先將字符串轉化為毫秒值，計算差值，然后轉化為天數

<script>
    window.onload = function() {
        var str1 = "2020-04-17";
        var str2 = "2020-04-12";
        var day1 = new Date(str1);
        var day2 = new Date(str2);
        //console.log("day1:" + day1);
        //console.log("day2:" + day2);
        var differDay = Math.abs(day1-day2)/1000/60/60/24;
        console.log(differDay);
    }
</script>