JavaScript data types
String, Number, Boolean, Array, Object, Null, Undefined
1 <!DOCTYPE html> 2 <html> 3 <head lang="en"> 4 <meta charset="UTF-8"> 5 <title></title> 6 <script> 7 // The type of the variable is determined by the variable 8 // Weakly typed languages 9 10 // String types, those in quotes are called string types 11 // var userName = "ghostWu"; 12 // var userName= 'ghostWu'; 13 // How to check the type of a variable14 // typeof + the name of the variable15 // alert( typeof userName );//string161718 // var age = 20; 19 // alert(typeof age); //number(numeric type) 20 21 // var n = 0.2; 22 // alert( typeof n ); 23 24 25 // boolean ( true /false ) 26 // var a = true; 27 // alert( true ); 28 // alert( typeof true ); //boolean 29 // var a = false; 30 // alert( typeof a ); // boolean 31 32 // var a = 'true'; //string 33 // var a = 'false'; //string 34 // alert( typeof a ); 35 36 37 // object: object, a thing... 38 // var a = document; 39 // alert( typeof a ); //object(object) 40 41 // var a; 42 // alert( a ); //When declaring a variable, no value is given, then its value is undefined 43 // alert( typeof a ); //type (undefined); 44 45 46 // var a = null; 47 // alert( a ); 48 // alert( typeof null ); //null object 49 50 51 52 var a = 10; 53 a = '你好'; 54 alert( typeof a ); 55 56 57 58 59 </script> 60 </head> 61 <body> 62 63 </body> 64 </html>