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77、随机数函数 <!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> // 左闭右开 能取到0但取不到1 中间的随机一个小数 // console.log(Math.random()) // 0~10 之间的整数 // console.log(Math.floor(Math.random() * 11)) // let arr = ['red', 'green', 'blue'] // let random = Math.floor(Math.random() * arr.length) //3 // console.log(random) // console.log(arr[random]) // 取到 N ~ M 的随机函数 function getRandom(N, M){ return Math.floor(Math.random() * (M - N + 1)) + N } console.log(getRandom(4, 8)) </script> </body> </html> -
76、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 // floor 地板 向下取整 console.log(Math.floor(1.1))//1 console.log(Math.floor(1.1))//1 console.log(Math.floor(1.9))//1 // 四舍五入 round console.log(Math.round(1.1))//1 console.log(Math.round(1.5))// 2 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)) //最大值 5 console.log(Math.min(1,2,3,4,5)) // 最小值 1 console.log(Math.abs(-1)) //1 //null 类似 let obj = {} let obj = null // 空对象 </script> </body> </html>
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75、学生信息表素材 <!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> // 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'} ] //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>
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74、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>
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73、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: 'pink', age: 18, gender: '男' } // 2.遍历对象 for (let k in obj){ console.log(k) //属性名 字符串 加引号的 // console.log(obj.k) //undefined console.log(obj[k]) } </script> </body> </html>
