js递归和数组去重(简单便捷的用法)

1.递归例子
<script type="text/javascript">
    function test(num) {
        if(num < 0) {
            return;
        }
        console.log('递归算法');
        test(num - 1);
    }
    test(8);  //打印九次 递归算法；
</script>

2.递归求和 1-100
<script type="text/javascript">
    function Sum(num) {
        if(num < 1) {
            return num = 0;
        }
        console.log('递归算法'); //打印100次
        return Sum(num - 1) + num
    }
    var a = Sum(100)
    console.log(a) //结果是5050；
</script>

3.递归阶乘 5 （5*4*3*2*1）
<script type="text/javascript">
    function Sum(num) {
        if(num <= 1) {
            return 1;
        }
        console.log('递归算法');
        return num*Sum(num - 1); //5 4 3 2 1 0
    }
    var a = Sum(5);
    console.log(a); //120
</script>

4.数组去重 indexOf()
<script type="text/javascript">
    var arr = [1, 2, 3, 4, 3, 6, 78, 8];
    function dele() {
        var newArry = [];
        for(var i = 0; i < arr.length; i++) {
            if(newArry.indexOf(arr[i]) == -1) {
                newArry.push(arr[i])
            }
        }
        console.log(newArry) //[1, 2, 3, 4, 6, 78, 8];
    }
    dele();
</script>

5.拓展运算符(...)内部使用for...of循环
<script type="text/javascript">
    let arr = [1, 2, 2, 3, 3];
    let newArry = [...new Set(arr)];
    console.log(newArry); //[1,2,3]
</script>