数组

arr.filter()
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let arr = [12, 5, 8, 99, 27, 24, 30, 13];

        let arr2 = arr.filter(item => {
            if (item % 2 == 0) {
                return false;
            } else {
                return true;
            }
        })
        console.log(arr);
        console.log(arr2);
    </script>
</head>

<body>

</body>

</html>

arr.filter2
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let arr = [12, 5, 8, 99, 27, 24, 30, 13];

        let arr2 = arr.filter(item => item % 2 == 0);
        console.log(arr);
        console.log(arr2);
    </script>
</head>

<body>

</body>

</html>

arr.forEach()
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let arr = [12, 5, 8, 99, 27, 24, 30, 13];

        arr.forEach((item, index) => {
            // console.log('第' + index + '个是：' + item);
            console.log(`第${index}个是${item}`);
        });
    </script>
</head>

<body>

</body>

</html>

arr.map()
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let arr = [12, 5, 8, 99, 27, 24, 30, 13];

        let arr2 = arr.map(item => {
            return item * 2;
        });

        console.log(arr);
        console.log(arr2);
    </script>
</head>

<body>

</body>

</html>

arr.map2
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let arr = [12, 5, 8, 99, 27, 24, 30, 13];

        let arr2 = arr.map(item => item * 2);


        console.log(arr);
        console.log(arr2);
    </script>
</head>

<body>

</body>

</html>

arr.reduce()
求和
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let arr = [12, 5, 8, 99, 27, 24, 30, 13];

        let result = arr.reduce((tmp, item, index) => {
            return tmp + item;
        });


        console.log(arr);
        console.log(result);
    </script>
</head>

<body>

</body>

</html>

arr.reduce2
求平均数
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let arr = [12, 5, 8, 99, 27, 24, 30, 13];

        let result = arr.reduce((tmp, item, index) => {
            if (index < arr.length - 1) {
                return tmp + item;
            } else {
                return (tmp + item) / arr.length;
            }
        });


        console.log(arr);
        console.log(result);
    </script>
</head>

<body>

</body>

</html>
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