<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>演示JS中的运算</title> </head> <body> <script type="text/javascript"> var num = "21"; num = num + 5; alert(num) var t = "x"; t = t - 1; alert(t) var x = 3; x = x++; alert(x); </script> </body> </html>