JavaScript学习 — 数组

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创建数组

<script>
    // 创建一个字符串数组
    let arr0 = ['路飞', '索隆', '山治'];
    // 输出该数组
    window.console.log(arr0);
    // 根据下标读取元素
    window.console.log(arr0[0]);
    window.console.log(arr0[1]);
    window.console.log(arr0[2]);
    // 无此元素会显示未定义（undefined）
    window.console.log(arr0[3]);
    // 为下标3赋值
    arr0[3] = '乌索普';
    window.console.log(arr0[3]);
    // 输出该数组的长度
    window.console.log(arr0.length);
    // 输出该数组
    window.console.log(arr0);
</script>

遍历数组

<script>
    let array = ['路飞', '索隆', '山治'];
    // 使用for循环遍历
    for (let index = 0; index < array.length; index++) {
        const element = array[index];
        window.console.log(element);
    }
    window.console.log('+++++++++++++++++++++++++++++++++++++++');
    // 使用foreach遍历
    array.forEach(element => {
        window.console.log(element);
    });
    window.console.log('+++++++++++++++++++++++++++++++++++++++');
    // 使用for in遍历的是数组的下标
    for (const index in array) {
        window.console.log(index);
    }
    window.console.log('+++++++++++++++++++++++++++++++++++++++');
    for (const index in array) {
        window.console.log(array[index]);
    }
    window.console.log('+++++++++++++++++++++++++++++++++++++++');
    // 使用for of 遍历
    for (const element of array) {
        window.console.log(element);
    }
</script>

列表生成式

<script>
    let nums = [0, 2, 5, 6, 8];
    // 判断是否为偶数数组
    let res01 = nums.every(num => {
        return num % 2 == 0;
    });
    console.log(res01);
    // 过滤数组中的数据
    let res02 = nums.filter(num => num % 2 == 0);
    console.log(res02);
    // 将数组中的每个元素操作
    let res03 = nums.map(num => num * 2);
    console.log(res03);
    // 求数组元素的和
    let res04 = nums.reduce((a, b) => a + b);
    console.log(res04);
    // 更改数组元素间的拼接符
    let res05 = nums.join('—');
    console.log(res05);
    let strs = ['王', '路', '飞'];
    let res06 = strs.join('');
    console.log(res06);
    let times = [1998, 08, 17];
    let date = times.join('-');
    console.log(date);
</script>

操作数组

数组新增和删除元素：

<script>
    let array = ['路飞', '索隆'];
    window.console.log(array);
    // 数组末尾追加元素
    array[array.length] = '山治';
    window.console.log(array);
    // 数组末尾追加元素
    array.push('乌索普');
    window.console.log(array);
    // 在数组起始位置插入元素
    array.unshift('娜美');
    window.console.log(array);
    // 以弹栈的方式获取数组最大下标位置上的元素
    let a = array.pop();
    window.console.log(a);
    window.console.log(array);
    // 以弹栈的方式获取数组最小下标位置上的元素
    let b = array.shift();
    window.console.log(b);
    window.console.log(array);
</script>

数组的截取slice：

<script>
    let array = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
    console.log(array);
    // slice(起始index,结束index) 注意不包含结束index位置上的元素
    let newArr = array.slice(3, 8);
    console.log(newArr);
    console.log(array);
</script>

数组的截取splice：

<script>
    let array = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
    console.log(array);
    // splice(起始index,截取长度)
    let newArr = array.splice(4, 4);
    console.log(newArr);
    console.log(array);
    let array1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
    // splice(起始index,截取长度,....添加输入的元素到原数组中)
    newArr1 = array1.splice(3, 7, '路飞', '索隆', '山治');
    console.log(newArr1);
    console.log(array1);
</script>