1.倒计时效果

<script>
        function countDown(time) {
            var nowTime = +new Date();
            var inputTime = +new Date(time);
            var times = (inputTime - nowTime) / 1000;
            var d = parseInt(times / 60 / 60 / 24); //  计算天数
            d = d < 10 ? '0' + d : d;
            var h = parseInt(times / 60 / 60 % 24) //   计算小时
            h = h < 10 ? '0' + h : h;
            var m = parseInt(times / 60 % 60); //   计算分数
            m = m < 10 ? '0' + m : m;
            var s = parseInt(times % 60); //   计算当前秒数 
            s = s < 10 ? '0' + s : s;
            return d + '天' + h + '时' + m + '分' + s + '秒';
        }
        console.log(countDown('2022-2-28 00:00:00'));
</script>

2.筛选数组：有一个包含工资的数组[1500, 1200, 2000, 2100, 1800]，要求把数组中工资超过2000的删除，剩余的放到新数组里面

<script>
        var arr = [1500, 1200, 2000, 2100, 1800];
        var newArr = [];
        for (var i = 0; i < arr.length; i++) {
            if (arr[i] < 2000) {
                newArr[newArr.length] = arr[i];   //或：newArr.push(arr[i]);
            }
        }
        console.log(newArr);
</script>

3.数组去重：有一个数组[‘c’, ‘a’, ‘z’, ‘a’, ‘x’, ‘a’, ‘x’, ‘c’, ‘b’]，要求去除数组中重复的元素。

<script>
        function unique(arr) {
            var newArr = [];
            for (var i = 0; i < arr.length; i++) {
                if (newArr.indexOf(arr[i]) === -1) {
                    newArr.push(arr[i]);
                }
            }
            return newArr;
        }
        var demo = unique(['c', 'a', 'z', 'a', 'x', 'a', 'x', 'c', 'b']);
        console.log(demo);
</script>