javascript - 为什么这个简单的 javascript 程序不起作用？

Question

警报窗口给我消息 NaN 出了什么问题？感谢所有的帮助

var weight = parseFloat(document.BMI.weight.value)
var height = parseFloat(document.BMI.height.value)

function calcBMI() {
var answer = weight * 703 / (height*height)
return answer;
  }
    </script>


 <form action="" name="BMI">
<input type="text" name="weight" />
<input type="text" name="height" />
<input type="submit" onclick="alert(calcBMI())" />
</form>

Answer 1

<script type="text/javascript">
function calcBMI() {
var weight = parseFloat(document.BMI.weight.value)
var height = parseFloat(document.BMI.height.value)
var answer = weight * 703 / (height*height)
return answer;
  }
    </script>


 <form action="" name="BMI">
<input type="text" name="weight" />
<input type="text" name="height" />
<input type="submit" onclick="alert(calcBMI())" />
</form>

希望它现在可以工作:)

Answer 2

您需要将变量移动到函数调用中。*编辑..我被打败了。

<form action="" name="BMI">
  <input type="text" name="weight" />
  <input type="text" name="height" />
  <input type="submit" onclick="alert(calcBMI())" />
</form>

<script type="text/javascript">

function calcBMI() {
    var weight = parseFloat(document.BMI.weight.value)
    var height = parseFloat(document.BMI.height.value)
    var answer = weight * 703 / (height*height)
    console.log(weight);
    return answer;
}
</script>

Answer 3

    function calcBMI() {
    var weight = parseFloat(document.BMI.weight.value)
var height = parseFloat(document.BMI.height.value)
var answer = weight * 703 / (height*height)
return answer;
  }
    </script>

局部变量和全局变量存在问题。当您单击按钮时，该功能不会从文本框中获取值