<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> </head> <body> <input type="text" id="number1"> <select id="selector"> <option selected>+</option> <option>-</option> <option>*</option> <option>/</option> </select> <input type="text" id="number2"> = <span id="result"></span> <input type="button" onclick="calc()" value="计算"> <script> function calc(){ //获取编辑框1.内容 let num1 = document.getElementById("number1").value; //判断是否为空 if(num1===""){alert("请输入第一个数");return ;} //判断是否为数字 if(isNaN(num1)){alert("请在第一个输入框输入一个数字");return ;} //获取编辑框2.内容 let num2 = document.getElementById("number2").value; if(num2===""){alert("请输入第二个数");return ;} if(isNaN(num2)){alert("请在第二个输入框输入一个数字");return ;} //获取运算符号 let t = document.getElementById("selector").value; //获取第三个编辑框以便计算后显示运算结果 let result = document.getElementById("result"); //将字符串转为数字 try{ num1 = parseFloat(num1) num2 = parseFloat(num2) }catch (err){ alert(err.message) return ; } //当做除法时,除数不能为0 if(t==="/" && num2===0) { alert("除数不能为0") return; } //根据运算符选择相应的计算 switch (t){ case '+': result.innerText = (num1+num2).toString(); break; case '-': result.innerText = (num1-num2).toString(); break; case '*': result.innerText = (num1 * num2).toString(); break; case '/': result.innerText = (num1 / num2).toString(); break; default: result.innerText = "what happen?" } return result.innerText; } </script> </body> </html>