<!DOCTYPE html> <html> <head> <title> 事件</title> <script type="text/javascript"> function count(){ //获取第一个输入框的值 var x=parseInt(document.getElementById("txt1").value); //获取第二个输入框的值 var y=parseInt(document.getElementById("txt2").value); //获取选择框的值 var myselect=document.getElementById("select"); var index=myselect.selectedIndex; var selectedvalue=myselect.options[index].value; var result=0; //获取通过下拉框来选择的值来改变加减乘除的运算法则 switch(selectedvalue){ case "+": result=x+y; break; case "-": result= x-y; break; case "*": result= x*y; break; case "/": result= x/y; } //设置结果输入框的值 document.getElementById("fruit").value = result ; } </script> </head> <body> <input type='text' id='txt1' /> <select id='select'> <option value='+'>+</option> <option value="-">-</option> <option value="*">*</option> <option value="/">/</option> </select> <input type='text' id='txt2' /> <input type='button' value=' = ' onclick="count()"/> <!--通过 = 按钮来调用创建的函数，得到结果--> <input type='text' id='fruit' /> </body> </html>