当我在浏览器中打开它时，我可以输入我想要的方程式，但在显示答案后我无法重置计算器。当我得到 NaN 后，我陷入困境。任何帮助将非常感激。谢谢
<!DOCTYPE html>
<HTML>
<HEAD>
<script type = "text/javascript">
function divide()
{
document.calculator.output.value += "/";
}
function add()
{
document.calculator.output.value += "+";
}
function num9()
{
document.calculator.output.value += "9";
}
function num8()
{
document.calculator.output.value += "8";
}
function num7()
{
document.calculator.output.value += "7";
}
function multiply()
{
document.calculator.output.value += "*";
}
function percent()
{
document.calculator.output.value += "%";
}
function num6()
{
document.calculator.output.value += "6";
}
function num5()
{
document.calculator.output.value += "5";
}
function num4()
{
document.calculator.output.value += "4";
}
function subtr()
{
document.calculator.output.value += "-";
}
function num3()
{
document.calculator.output.value += "3";
}
function num2()
{
document.calculator.output.value += "2";
}
function num1()
{
document.calculator.output.value += "1";
}
function numZero()
{
document.calculator.output.value += "0";
}
function buildFormula()
{
var evalu= alert(eval(document.calculator.output.value)) + document.clear();
document.calculator.output.value= evalu;
}
</script>
</HEAD>
<BODY>
<form name="calculator">
<table border=0>
<tr>
<td colspan=4><input type=text readonly=true name="output" size = 25></td>
</tr>
<tr>
<td><input type=button value= " 7 " onClick="num7()"></td>
<td><input type=button value= " 8 " onClick="num8()"></td>
<td><input type=button value= " 9 " onClick="num9()"></td>
<td><input type=button value= " / " onClick="divide()"></td>
<td><input type=button value= " + " onClick="add()"></td>
</tr>
<tr>
<td><input type=button value= " 4 " onClick="num4()"></td>
<td><input type=button value= " 5 " onClick="num5()"></td>
<td><input type=button value= " 6 " onClick= "num6()"></td>
<td><input type=button value= " * " onClick= "multiply()"></td>
<td><input type=button value= " % " onClick="percent()"></td>
</tr>
<tr>
<td><input type=button value = " 1 " onClick="num1()"></td>
<td><input type=button value = " 2 " onClick="num2()"></td>
<td><input type=button value = " 3 " onClick="num3()"></td>
<td><input type=button value = " - " onClick="subtr()"></td>
<td><input type=button value = " = " onClick="buildFormula()"></td>
</tr>
<tr>
<td colspan=5><input type=button value = " 0 " onClick="numZero()"></td>
</tr>
</table>
</form>
</BODY>
</HTML>
最佳答案
您的问题是因为您试图将 alert 的返回与 document.clear() 的返回进行汇总 - 这是错误的，alert 不返回任何内容，而 document.clear 是未定义的方法
将您的功能更改为这个:
function buildFormula()
{
var evalu= eval(document.calculator.output.value);
document.calculator.output.value= '';
alert(evalu);
}
关于给出答案后，Javascript 计算器不会清除，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19696548/