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13、字符串类型 <!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 str = 'pink' let str1 = "pink" let str2 = `中文` console.log(str2); // 字符串的拼接 console.log(1 + 1); console.log('我叫' + '坤坤');//太麻烦不建议使用 </script> </body> </html> -
12、数字数据类型和算术运算符 <!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> // 计算圆面积案例 // 1、页面弹出输入框 let r = prompt("请输入圆的半径:") // 2、计算圆的面积（内部处理） let re = 3.14 * r * r // 3、页面输出 document.write(re) // NaN not a Number不是一个数字 console.log("小坤" - 2); console.log(NaN + 2); </script> </body> </html>
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11、常量 <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width= , initial-scale=1.0"> <title>Document</title> </head> <body> <script> // 常量 1.不允许更改值 const PI = 3.14 console.log(PI); // 不会变 // 2.常量声明的时候必须赋值 // 不需要重新赋值的数据用const </script> </body> </html>
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10、数组 <!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 = [10,20,30,40] // 1、声明数组 let arr = ["小蔡","小徐","小坤"] // 2。使用数组 数组名[索引号] 从0 // console.log(arr) consloe.log(arr[0])//小蔡 console.log(arr[2]) // 数组长度 = 索引号+1 console.log(arr.length);//3 </script> </body> </html>
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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>
