find(),findIndex(),includes()的使用

find() 方法返回数组中满足提供的测试函数的第一个元素的值。否则返回 undefined

<script>
        //find()方法
            let arr = [2, 3, 4, 5, 34, 45, 56, 78, 56, 78, 89, 80];
            let newArray3 = arr.find(item => item > 5);
            console.log(newArray3);//输入的是满足大于5的第一个数所以是34

            //不满足的情况下输出undefined
            let arr1 = [2, 3, 4, 5];
            let newArray4 = arr1.find(item => item > 5);
            console.log(newArray4);//不满足条件输入undefined
    </script>

findIndex()方法返回数组中满足提供的测试函数的第一个元素的索引。若没有找到对应元素则返回-1

<script>
        //findIndex()方法
        //满足返回大于10的索引值34从零开始也就是4
        let arr = [2,3,4,5,34,45,56,78,56,78,89,80];
        let newArray4 = (item => item>10);
        console.log(arr.findIndex(newArray4));

        //不满足返回-1
        let arr1 = [2,3,4,5,];    
        let newArray5 = (item => item>10);
        console.log(arr1.findIndex(newArray5));
    </script>

includes() 方法用来判断一个数组是否包含一个指定的值，根据情况，如果包含则返回 true，否则返回false

<script>
        //includes()
        let arr = [2,3,4,5,34,45,56,78,56,78,89,80];
        //包含2返回ture
        console.log(arr.includes(2));
        //不包含返回false
        console.log(arr.includes(1));
    </script>