1 <!DOCTYPE html> 2 <html> 3 <head> 4 <meta charset="utf-8"> 5 <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> 6 <title>练习</title> 7 <style type="text/css"> 8 #box{width: 300px;height: 300px;background: yellow;margin:10px auto;} 9 </style> 10 </head> 11 <body> 12 <input type="button" value="点击" onclick="alert('1')";> 13 <input type="button" value="点击2" onclick="alert(2)";> 14 <input type="button" value="点击3" onclick="alert(1+2)";> 15 <input type="button" value="点击4" onclick="alert('1'+'2')";> 16 <input type="button" value="点击5" onclick="alert('1'+2)";> 17 18 <input type="button" value="点击6" onclick="alert(我)";> 19 <input type="button" value="点击7" onclick="alert('我')";> 20 </body> 21 </html>
alert中带引号的是字符串，不带引号的是变量，变量必须先定义，所以，不带引号的我，将无法弹出来