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9、检测数据类型 <!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> <script> var a = 100 console.log(typeof a) //转成数值 console.log(typeof(a)) // 结果一定是字符串，string类型 console.log(typeof typeof a) console.log(typeof a + 100) console.log(typeof (a + 100)) </script> </head> <body> </body> </html> -
8、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> <script> // 1.基本类型 /* 1.Number数字类型 2.5(浮点数)，2e，十六进制，二进制 ， 2.String字符串类型 写的是什么结果就是什么 3.Boolean true false 布尔值 4.Undefind 5.Null 空的意思 6.Sys */ // 2.复杂类型(对象类型) // number var age = 18 // console.log(age+20) // 浮点数 var price = 12.5 console.log(price) var year = 2e3 //10的三次方 2000 科学计数法 console.log(year) var a = 0x99 //十六进制 9x16+9 1-9，a，b，c，d，e，f， console.log(a) var a = 0xff console.log(a) var b = 077 //7x8+7 八进制 console.log(b) var c = 0b11 //二进制 1x2+1 console.log(c) var num1 = 10 var num2 = "20" console.log(num1+num2) //类型转换 var str = "hello" //字符串加引号 console.log(str) var ischecked = false console.log(ischecked) var which //声明了，但是未赋值,未来可以给任意的值 console.log(which) which = 100 console.log(which) var whichobject = null //未来明确给我的值 whichobject = {name:"yu"} console.log(whichobject) </script> </head> <body> 记住用户名<input type="checkbox"> </body> </html>
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7、规则 <!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> <script> var al,a2;a_;a$b; // var A1 大小写不一样 // console.log() var age , email;name // var spms = 10 var goodNumber //驼峰 // var god_number </script> </head> <body> </body> </html>
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6、JS的变量 <!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>变量</title> <script> // var x //定义变量不赋值 // x = 100 //从输入框内获取 // var y = x + 2000 //定义变量赋值 // console.log(y) // var x,y,z // var a=1,b=2,c=3 // // 括号中加双引号是变量，不加是字符 // let age // // 赋值 = 赋值 // age = 18 // // 输出age变量 // console.log(age) // let age = 18, uname = "kunkun" // console.log(age,uname); // 提倡声明的方式 let age = 17 let uname = "kun" console.log(age,uname) </script> </head> <body> </body> </html>
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5、JS的注释与规范 <!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> <script> alert("你好js") // console.log("helloworld") document.write("javascript我来了") console.log('查询成功') // 输出内容到网页 // document.write("helloworld") //输入语句 // prompt("请输入你的年龄") // </script> </head> <body> </body> </html
