前端JavaScript入门到精通，javascript核心进阶ES6语法、API、js高级等基础知识和实战 —

允许一切发生，生活不过是见招拆招。

思维导图

一、循环-for

1.1 for 循环-基本使用

<!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>
    // 利用for循环输出三句话 月薪过万
    for (let i = 1; i <= 3; i++) {
      document.write('月薪过万<br>')
    }
    // 课堂练习： 输出10句月薪过万，并说出for循环的执行过程
  </script>
</body>

</html>

<!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>
    // 1. 输出1~100岁
    // for (let i = 1; i <= 100; i++) {
    //   document.write(`今年我${i}岁了 <br>`)
    // }
    // 2. 求1~100之间的偶数和
    // let sum = 0
    // for (let i = 1; i <= 100; i++) {
    //   if (i % 2 === 0) {
    //     // 把i加到sum里面去
    //     // sum = sum + i
    //     sum += i
    //   }
    // }
    // document.write(`1~100之间的偶数和是: ${sum}`)
    // 3. 页面打印5个小星星
    // for (let i = 1; i <= 5; i++) {
    //   document.write('★')
    // }
    // 4. 打印数组
    let arr = ['刘德华', '刘晓强', '刘晓庆', '刘若英', '刘热巴', 'pink老师']
    // console.log(arr[0])
    // console.log(arr[1])
    // console.log(arr[2])
    // console.log(arr[3])
    // i <= 4    长度 - 1
    // for (let i = 0; i <= arr.length - 1; i++) {
    //   console.log(arr[i])
    // }
    // 必须从0开始，因为数组索引号从0开始  arr.length = 6
    // 遍历数组 ：  从第一个循环到最后一个
    for (let i = 0; i < arr.length; i++) {
      console.log(arr[i])
    }

    let arr1 = []
    console.log(arr1)
    console.log(arr1[0]) // undefined
    console.log(arr1[1]) // undefined
  </script>
</body>

</html>

<!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 (let i = 1; i <= 5; i++) {
    //   if (i === 3) {
    //     continue  // 退出本次循环，本次循环中 continue下面的语句不在执行
    //   }
    //   console.log(i)
    //   document.write(i)
    // }

    // for (let i = 1; i <= 5; i++) {
    //   if (i === 3) {
    //     break  // 退出整个循环 结束循环
    //   }
    //   console.log(i)
    //   document.write(i)
    // }
    // 无限循环
    for (; ;) {
      console.log(11)
    }
  </script>
</body>

</html>

1.2 for 循环嵌套

<!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>
    // 外层循环打印 第 n 天
    for (let i = 1; i <= 3; i++) {
      document.write(`第${i}天<br>`)
      // 里层循环打印 第几个单词
      for (let j = 1; j <= 5; j++) {
        document.write(`记住了第${j}个单词<br>`)
      }
    }
  </script>
</body>

</html>

<!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>
    // // 外层循环打印行数
    // for (let i = 1; i <= 5; i++) {
    //   // 里层循环打印几个星星
    //   for (let j = 1; j <= 5; j++) {
    //     document.write('☆')
    //   }
    //   // 进行换行显示
    //   document.write('<br>')
    // }

    let row = +prompt('请输入行数:')
    let col = +prompt('请输入列数:')
    // 外层循环打印行数
    for (let i = 1; i <= row; i++) {
      // 里层循环打印几个星星
      for (let j = 1; j <= col; j++) {
        document.write('☆')
      }
      // 进行换行显示
      document.write('<br>')
    }
  </script>
</body>

</html>

<!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>
    // 1. 外层循环控制行数
    for (let i = 1; i <= 5; i++) {
      // 2. 里层循环控制列数（几个星星）
      for (let j = 1; j <= i; j++) {
        document.write('◆')
      }
      // 换行
      document.write('<br>')
    }

  </script>
</body>

</html>

<!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>
  <style>
    span {
      display: inline-block;
      width: 100px;
      padding: 5px 10px;
      border: 1px solid pink;
      margin: 2px;
      border-radius: 5px;
      box-shadow: 2px 2px 2px rgba(255, 192, 203, .4);
      background-color: rgba(255, 192, 203, .1);
      text-align: center;
      color: hotpink;
    }
  </style>
</head>

<body>

  <script>
    // 1. 外层循环控制行数
    for (let i = 1; i <= 9; i++) {
      // 2. 里层循环控制列数
      for (let j = 1; j <= i; j++) {
        document.write(`<span>${j} X ${i} = ${i * j}</span>`)
      }
      // 换行
      document.write('<br>')
    }

  </script>
</body>

</html>

二、数组

2.1 数组是什么

2.2 数组的基本使用

2.2.4. 遍历数组(重点)

<!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 arr = [2, 6, 1, 7, 4]
    // 1. 求和的变量 sum
    let sum = 0
    // 2.遍历累加
    for (let i = 0; i < arr.length; i++) {
      // console.log(arr[i])
      // sum = sum + arr[i]
      sum += arr[i]
    }
    console.log(`数组的和的结果是: ${sum}`)
    // 3. 平均值  和 / arr.length  = 4
    console.log(`数组的平均值结果是: ${sum / arr.length}`)


    // sum = sum + arr[0]
    // console.log(sum) 
  </script>
</body>

</html>

<!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 arr = [2, 6, 1, 7, 400, 55, 88, 100]
    // max里面要存的是最大值
    let max = arr[0]
    // min 要存放的是最小值
    let min = arr[0]
    // 遍历数组
    for (let i = 1; i < arr.length; i++) {
      // 如果max 比 数组元素里面的值小，我们就需要把这元素赋值给 max
      // if (max < arr[i]) max = arr[i]
      max < arr[i] ? max = arr[i] : max
      // 如果min 比 数组元素大， 我们就需要把数组元素给min
      // if (min > arr[i]) {
      //   min = arr[i]
      // }
      min > arr[i] ? min = arr[i] : min
    }
    // 输出 max
    console.log(`最大值是: ${max}`)
    console.log(`最小值是: ${min}`)
  </script>
</body>

</html>

2.3 操作数组

改

<!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 arr = []
    // console.log(arr)
    // // console.log(arr[0])  // undefined
    // arr[0] = 1
    // arr[1] = 5
    // console.log(arr)
    let arr = ['pink', 'red', 'green']
    // 修改
    // arr[0] = 'hotpink'
    // console.log(arr)
    // 给所有的数组元素后面加个老师  修改
    for (let i = 0; i < arr.length; i++) {
      // console.log(arr[i])
      arr[i] = arr[i] + '老师'
    }
    console.log(arr)

  </script>
</body>

</html>

<!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>
    // 重点案例
    let arr = [2, 0, 6, 1, 77, 9, 54, 3, 78, 7]
    // 1. 声明新的空的数组
    let newArr = []
    // 2. 遍历旧数组
    for (let i = 0; i < arr.length; i++) {
      if (arr[i] >= 10) {
        // 3. 满足条件 追加给新的数组
        newArr.push(arr[i])
      }
    }
    // 4. 输出新的数组
    console.log(newArr)
  </script>
</body>

</html>

<!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 arr = [2, 0, 6, 1, 77, 0, 52, 0, 25, 7]
    // 1. 声明一个新的数组
    let newArr = []
    // 2. 遍历筛选
    for (let i = 0; i < arr.length; i++) {
      if (arr[i] !== 0) {
        newArr.push(arr[i])
      }
    }
    // 输出新数组
    console.log(newArr)
  </script>
</body>

</html>

三、综合案例

<!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>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .box {
            display: flex;
            width: 700px;
            height: 300px;
            border-left: 1px solid pink;
            border-bottom: 1px solid pink;
            margin: 50px auto;
            justify-content: space-around;
            align-items: flex-end;
            text-align: center;
        }

        .box>div {
            display: flex;
            width: 50px;
            background-color: pink;
            flex-direction: column;
            justify-content: space-between;
        }

        .box div span {

            margin-top: -20px;
        }

        .box div h4 {
            margin-bottom: -35px;
            width: 70px;
            margin-left: -10px;
        }
    </style>
</head>

<body>




    <script>
        // 1. 四次弹框效果
        // 声明一个新的数组
        let arr = []
        for (let i = 1; i <= 4; i++) {
            // let num = prompt(`请输入第${i}季度的数据:`)
            // arr.push(num)
            arr.push(prompt(`请输入第${i}季度的数据:`))
            // push记得加小括号，不是等号赋值的形式
        }
        // console.log(arr)  ['123','135','345','234']
        // 盒子开头
        document.write(` <div class="box">`)

        // 盒子中间 利用循环的形式  跟数组有关系
        for (let i = 0; i < arr.length; i++) {
            document.write(`
              <div style="height: ${arr[i]}px;">
                <span>${arr[i]}</span>
                <h4>第${i + 1}季度</h4>
              </div>          
            `)
        }
        // 盒子结尾
        document.write(` </div>`)
    </script>
</body>

</html>

冒泡排序

<!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 arr = [5, 4, 3, 2, 1]
    let arr = [2, 4, 3, 5, 1]
    // for (let i = 0; i < arr.length - 1; i++) {
    //   for (let j = 0; j < arr.length - i - 1; j++) {
    //     // 开始交换 但是前提 第一个数大于第二个数才交换
    //     if (arr[j] > arr[j + 1]) {
    //       // 交换2个变量
    //       let temp = arr[j]
    //       arr[j] = arr[j + 1]
    //       arr[j + 1] = temp
    //     }
    //   }
    // }
    // arr.sort()  // 排序
    // sort 升序排列
    // arr.sort(function (a, b) {
    //   return a - b
    // })
    // sort() 降序
    arr.sort(function (a, b) {
      return b - a
    })
    console.log(arr)

    // let num1 = 10
    // let num2 = 20
    // let temp = num1
    // num1 = num2
    // num2 = temp 
  </script>
</body>

</html>