Javascript 如何使用 window.prompt 获取变量中的数学表达式？

Question

我有此代码，但无法正常工作。如您所见，我尝试将公式放入数组中。这用于稍后计算数学用途。但是程序没有将公式放在变量所在的正确位置：

<html>
<title> JavaScript Tutorial 1
</title>
<body>
<script language = "javascript">

var f, a, b, c, d, j, k, sum;

f = String(window.prompt("Formel"));
a = Number(window.prompt("untere grenze 1tes E"));
b = Number(window.prompt("obere grenze 1tes E"));
c = Number(window.prompt("untere grenze 2tes E"));
d = Number(window.prompt("obere grenze 2tes E"));





sum = 0;
for (j = a; j <= b; j++) {

    for (k = c ; k <= d ; k++) {
    sum += f;
    }
}

document.write(sum);

</script>
<noscript>
    <p> You have JavaScript Turned Off <p>
</noscript>
</body>
</html>

我这里有这段代码，计算正确。但我想将公式输入到 window.promp

的 var 中

<html>
<title> JavaScript Tutorial 1
</title>
<body>
<script language = "javascript">

var f, a, b, c, d, j, k, sum;

//f = String(window.prompt("Formel"));
a = Number(window.prompt("untere grenze 1tes E"));
b = Number(window.prompt("obere grenze 1tes E"));
c = Number(window.prompt("untere grenze 2tes E"));
d = Number(window.prompt("obere grenze 2tes E"));

sum = 0;
for (j = a; j <= b; j++) {

    for (k = c ; k <= d ; k++) {
    sum += j * j * k;
    }
}

document.write(sum);

</script>
<noscript>
    <p> You have JavaScript Turned Off <p>
</noscript>
</body>
</html>

Answer 1

@ yellowsir，感谢您的输入，它与 eval 配合使用效果很好，我理解安全性不足。因为我只是自己使用这个项目，所以不会有人输入恶意代码的风险；）

这是我从您的输入中得到的解决方案：

<html>
<title> JavaScript Tutorial 1
</title>
<body>
<script language = "javascript">

var f, a, b, c, d, j, k, sum;

a = Number(window.prompt("untere grenze 1tes E"));
b = Number(window.prompt("obere grenze 1tes E"));
c = Number(window.prompt("untere grenze 2tes E"));
d = Number(window.prompt("obere grenze 2tes E"));
f = window.prompt("Formel");

sum = 0;
for (j = a; j <= b; j++) {

    for (k = c ; k <= d ; k++) {
    sum += eval(f);
    }
}

// document.write("<br>")
document.write(sum);

</script>
<noscript>
<p> You have JavaScript Turned Off <p>
</noscript>
</body>
</html>

希望一切都清楚，请不要犹豫。

Javascript 如何使用 window.prompt 获取变量中的数学表达式？

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