1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <meta name="viewport" content="width=device-width, initial-scale=1.0"> 6 <meta http-equiv="X-UA-Compatible" content="ie=edge"> 7 <title>javascript逻辑非</title> 8 <!-- 9 逻辑或（!）个人理解： 10 前提条件： 11 -逻辑非只会返回布尔值 12 1）!n表否 13 2）!!n双重否定，表肯 14 --> 15 </head> 16 <body> 17 <script> 18 var a=1,b="2",c=0,d="abc",e="",f,g=a-d; 19 /* ! */ 20 console.log(!a);//false 21 console.log(!c);//true 22 /* !! */ 23 console.log(!!a);//true 24 console.log(!!c);//false 25 </script> 26 </body> 27 </html>