1、let
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> </head> <body> <script> //var 声明的变量往往会越域 //let 声明的变量有严格局部作用域 { var a = 1; let b = 2; } // console.log("===" a); // alert(a); alert(b); console.log(b); </script> </body> </html>2、结构表达式
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> </head>