<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> </head> <body> <input type="text" id="txt" value="1"/> <input type="button" onclick="add()" value="+"><input type="button" onclick="sub()" value="-"></td> <script> function add(){ var txt=document.getElementById("txt"); var a=txt.value; a++; txt.value=a; } function sub(){ var txt=document.getElementById("txt"); var a=txt.value; if(a>1){ a--; txt.value=a; }else{ txt.value=1; } } </script> </body> </html>
原文：http://www.cnblogs.com/zmsister/p/6567634.html