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18、显示转换 <!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 str = '123' // console.log(Number(str)); // console.log(Number('pink'));//错的 // let num = prompt('请输入年薪') // console.log(Number(num)); // // 保留整数（不会四舍五入 // console.log(parseInt('12px')); // console.log(parseInt('12.34px')); // console.log(parseInt('12.94px')); // //保留小数 // console.log(parseFloat('12px'));//12 // console.log(parseFloat('12.34px'));//12.34 // console.log(parseFloat('12.94px'));//12.94 // 案例 let inPutNumber = prompt('请输入第一个值：') let inPutNumber2 = prompt('请输入第二个值：') alert(`计算的结果：${Number(inPutNumber) + Number(inPutNumber2)}`) </script> </body> </html> -
17、隐式转换 <!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> // 任何数据和字符串相加结果都是字符串 console.log(1 + 1) console.log('pink' + 1) console.log(2 + 2) console.log(2 + '2')//22 加号不同 console.log(2 - 2) console.log(2 - '2')//0 console.log(+12) console.log(+'123') //+转换为数字型 </script> </body> </html>
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16、监测数据类型 <!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 console.log(typeof num); let str = 'pink' console.log(typeof str); let str1 = '10' console.log(typeof str1); let flag = false console.log(typeof flag); let un console.log(typeof un); let obj = null console.log(typeof null); let num1 = prompt('请输入第一个数:') </script> </body> </html>
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15、其他三种类型 <!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、true false 是布尔型字面量 // console.log(3 > 4); // let isCool = true // console.log(isCool); // 2、未定义类型 弱数据类型 声明一个变量未赋值就是 undefined // let num // console.log(num); // 3、null 空的 // let obj = null // console.log(obj) // 计算有区别 console.log(undefined + 1) //NaN console.log(null + 1) // 1 </script> </body> </html>
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14、模版字符串 <!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 age = 18 // // 模版字符串 外面是`` 外面是${变量名} // document.write(`我今年${age}岁了`) // 案例 let uname = prompt('请输入您的姓名:') let age = prompt('请输入您的年龄:') // 输出 document.write(`大家好，我叫${uname},今年${age}岁了`) </script> </body> </html>
