JS基础教程：2023.3.11第十三天-JavaScript对象的使用

前言

记录时间：2023.3.11

坚持的第十三天

JavaScript从入门到精通

学习javascript时间历程记录打卡

晚上8:00到22：00

JS基础对象总结

完成代码练习

1.遍历对象

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    // for in 我们不推荐遍历数组
    // let arr = ['pink', 'red', 'blue']
    // for (let k in arr) {
    //   console.log(k)  // 数组的下标 索引号  但是是字符串 '0'
    //   console.log(arr[k])  // arr[k]
    // }
    // 1. 遍历对象 for in   
    let obj = {
      uname: 'try栈',
      age: 18,
      gender: '男'
    }
    // 2. 遍历对象
    for (let k in obj) {
      console.log(k) // 属性名  'uname'   'age'
      // console.log(obj.uname)
      // console.log(obj.k)
      // console.log(obj.'uname')
      // console.log(obj['uname'])   'uname'  === k
      console.log(obj[k])  // 输出属性值  obj[k]
    }
  </script>
</body>

</html>

2.遍历数组对象

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    let students = [
      { name: '小明', age: 18, gender: '男', hometown: '河北省' },
      { name: '小红', age: 19, gender: '女', hometown: '河南省' },
      { name: '小刚', age: 17, gender: '男', hometown: '山西省' },
      { name: '小丽', age: 18, gender: '女', hometown: '山东省' }
    ]
    for (let i = 0; i < students.length; i++) {
      // console.log(i)  // 下标索引号
      // console.log(students[i]) // 每个对象
      console.log(students[i].name)
      console.log(students[i].hometown)
    }
  </script>
</body>

</html>

3.渲染学生信息表

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        table {
            width: 600px;
            text-align: center;
        }

        table,
        th,
        td {
            border: 1px solid #ccc;
            border-collapse: collapse;
        }

        caption {
            font-size: 18px;
            margin-bottom: 10px;
            font-weight: 700;
        }

        tr {
            height: 40px;
            cursor: pointer;
        }

        table tr:nth-child(1) {
            background-color: #ddd;
        }

        table tr:not(:first-child):hover {
            background-color: #eee;
        }
    </style>
</head>

<body>
    <h2>学生信息</h2>
    <p>将数据渲染到页面中...</p>

    <table>
        <caption>学生列表</caption>
        <tr>
            <th>序号</th>
            <th>姓名</th>
            <th>年龄</th>
            <th>性别</th>
            <th>家乡</th>
        </tr>
        <!-- script写到这里 -->
        <script>
            // 1. 数据准备
            let students = [
                { name: '小明', age: 18, gender: '男', hometown: '河北省' },
                { name: '小红', age: 19, gender: '女', hometown: '河南省' },
                { name: '小刚', age: 17, gender: '男', hometown: '山西省' },
                { name: '小丽', age: 18, gender: '女', hometown: '山东省' },
                { name: '晓强', age: 16, gender: '女', hometown: '蓝翔技校' }
            ]
            // 2. 渲染页面
            for (let i = 0; i < students.length; i++) {
                document.write(`
                <tr>
                    <td>${i + 1}</td>
                    <td>${students[i].name}</td>
                    <td>${students[i].age}</td>
                    <td>${students[i].gender}</td>
                    <td>${students[i].hometown}</td>
                </tr>
                `)
            }
        </script>
    </table>

</body>


</html>

4.数学内置对象Math

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    // 属性
    console.log(Math.PI)
    // 方法
    // ceil 天花板  向上取整
    console.log(Math.ceil(1.1)) // 2 
    console.log(Math.ceil(1.5)) // 2 
    console.log(Math.ceil(1.9)) // 2 
    // floor 地板  向下取整
    console.log(Math.floor(1.1))  // 1
    console.log(Math.floor(1.5))  // 1
    console.log(Math.floor(1.9))  // 1
    console.log(Math.floor('12px'))  // 1
    console.log('----------------')
    // 四舍五入 round
    console.log(Math.round(1.1))  // 1
    console.log(Math.round(1.49))  // 1
    console.log(Math.round(1.5))  // 2
    console.log(Math.round(1.9))  // 2
    console.log(Math.round(-1.1))  // -1 
    console.log(Math.round(-1.5))  // -1
    console.log(Math.round(-1.51))  // -2

    // 取整函数 parseInt(1.2)   // 1
    // 取整函数 parseInt('12px')   // 12

    console.log(Math.max(1, 2, 3, 4, 5))
    console.log(Math.min(1, 2, 3, 4, 5))
    console.log(Math.abs(-1));

    // null  类似 let obj = {}
    let obj = null 
  </script>
</body>

</html>

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