<!DOCTYPE html><html> <head> <meta charset="utf-8" /> <title></title> <script type="text/javascript"> function count(){ //获取第一个输入框的值 var txt1 = document.getElementById("txt1").value; //获取第二个输入框的值 var txt2 = document.getElementById("txt2").value; //获取选择框的值 var sel = document.getElementById("select").value; var num = ""; //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(sel){ case "+": num = txt1 + txt2; break; case "-": num = txt1 - txt2; break; case "*": num = txt1 * txt2; break; default: num = txt1 / txt2; } //设置结果输入框的值 document.getElementById("fruit").value = num; } </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>
