Array, function case

Knowledge points:

[Web front-end basics | JS basics] array
[web front-end basics | JS basics] function

Case 1: Flip the array

    <script>
        var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
        //创建一个空数组
        var newArr = [];
        // 遍历原数组
        for (var i = arr.length - 1; i >= 0; i--) {
    
    
            newArr[newArr.length] = arr[i];
        }
        console.log(newArr);
    </script>

Case 2: Function summation

    <script>
        function getSum(num1, num2) {
    
    
            var sum = 0;
            for (var i = num1; i <= num2; i++) {
    
    
                sum += i;
            }
            return sum;
        }
        console.log(getSum(1, 100));
        console.log(getSum(2, 5));
    </script>

Case 3: Find the largest of the three numbers

    <script>
        function getMax(num1, num2, num3) {
    
    
            //num1>num2,是的话把num1给max，不是的话把num2给max，再用1,2中最大和3同理去比较
            var max = num1 > num2 ? num1 : num2;
            max = num3 > max ? num3 : max;
            return max;
        }
        console.log(getMax(3, 4, 11));
    </script>

Case 4: Check whether the element exists in the array

<script>
    //检测元素是否存在于数组中,存在返回true,不存在返回false
    var str = "red";
    var arr = ['red', 'blue', 'green'];
    function check(str, arr) {
    
    
        for (var i = 0; i < 10; i++) {
    
    
            if (arr[i] == str) {
    
    
                return true;
            }
            else {
    
    
                return false;
            }
        }
    }
    console.log(check(str, arr));
</script>

Case 6: Array de-duplication

Haha, it shouldn’t be Baidu. I’m going to paste it. 12 kinds of js de-duplication methods, let’s find out

JavaScript array deduplication (12 methods, the most complete in history)

Case 7: Array to string

<script>
    // 需要一个新变量用于存放转换完的字符串str。
    // 遍历原来的数组，分别把里面数据取出来，加到字符串里面。
    // 同时在后面多加一个分隔符。
    var arr = ['red', 'green', 'blue', 'pink'];
    var str = '';//空字符串用来连接数组
    var sep = '！';//标记符可批量修改
    for (var i = 0; i < arr.length; i++) {
    
    
        str = str + arr[i] + sep;
    }
    console.log(str);
</script>

Case 8: Arguments find the maximum value of any number

<script>
    //arguments求任意个数最大值
    function getMax() {
    
    
        var max = arguments[0];
        for (var i = 1; i < arguments.length; i++) {
    
    
            if (arguments[i] > max) {
    
    
                max = arguments[i];
            }
        }
        return max;
    }
    console.log(getMax(1, 24, 2, 2, 34, 4, 52, 2));
</script>

Case 9: Determine whether it is a leap year

<script>
    //判断是否为闰年
    var year = prompt("请输入要查询的年份：")
    function isRunnian(year) {
    
    
        var flag = false;
        if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
    
    
            flag = true;
        }
        return flag;
    }
    alert(isRunnian(year));
</script>