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23、逻辑运算符 <!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> // 逻辑与 一假则假 console.log(true && true) console.log(false && true) console.log(2 < 3 && 4 > 3) console.log(1 < 2 && 3 > 4) console.log('---------------') // 逻辑或 一真则真 console.log(true || true) console.log(false || true) console.log(false || false) console.log('--------------') // 逻辑非 取反 console.log(!true)//false console.log(!false)//true </script> </body> </html> -
22、比较运算符 <!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> console.log(3 > 5) console.log(3 >= 3) console.log(2 == 2) // 比较运算符有隐式转换 把字符型的‘2’转换成数字类型的‘2’ 双等号只判断值 console.log(2 == '2') console.log(undefined == null)//true console.log(undefined === null)//false // 还判断数据类型 // 常用三等 === console.log(2 === '2') console.log(NaN === NaN) //NaN不等于任何人，包括他自己 console.log(2 !== '2')//true console.log(2 != '2')//false console.log('-------------------') console.log('a' < 'b')//true console.log('aa' < 'ab')//true </script> </body> </html>
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21、一元运算符 <!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 num = 10 // num = num + 1 // num += 1 // 1.前置自增 // let i = 1 // ++i // console.log(i) // 1.后缀自增 // let i = 1 // i++ // console.log(i) let i = 1 console.log(i++ + ++i + i) </script> </body> </html>
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20、赋值运算符 <!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 num = 1 // num = num + 1 // 采取赋值运算法 num += 3 console.log(num) </script> </body> </html>
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19、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> h2{ text-align: center; } table{ /* 合并相邻边框 */ border-collapse: collapse; height: 80px; margin: 0 auto; text-align: center; } th{ padding: 5px 30px; } table,th,td{ border: 1px solid #000; } </style> </head> <body> <h2>订单确认</h2> <script> //1、用户输入 let price = +prompt('请输入商品价格:') let num = +prompt('请输入商品数量:') let address = prompt('请输入收货地址:') //2、计算总额 let total = price * num // 3、页面打印渲染 document.write(` <table> <tr> <th>商品名称</th> <th>商品价格</th> <th>商品数量</th> <th>总价</th> <th>收获地址</th> </tr> <tr> <td>小米手机青春plus</td> <td>${price}</td> <td>${num}</td> <td>${total}</td> <td>${address}</td> </tr> </table> `) </script> </body> </html>
