Question

在提交时，在权重变量上检查非数字输入时，我的 if语句似乎无法正常工作。这是为什么？

   submitBtn.onclick = function(){

    var name = document.getElementById('name').value;
    var weight = document.getElementById('weight').value;
    var pound = weight * 2.20462;

    //Check that the value is a number
    if(isNan(weight)){
     alert("Please enter a number);
    }
   }

此处位于JsFiddle link

Answer 1

您的代码中存在多个问题：

您尝试在.onclick上调用submitBtn，这是未定义的。
您尝试拨打.isNan() .isNaN()
您不会关闭传递给alert()函数的字符串：

//Define submitBtn
var submitBtn = document.getElementById('submitBtn');
submitBtn.onclick = function(){

    var name = document.getElementById('name').value;
    var weight = document.getElementById('weight').value;
    var pound = weight * 2.20462;

    //Call isNaN()
    if(isNaN(weight)){

        //Close your string
        alert("Please enter a number");
    }
}

JSFiddle

Answer 2

您可以使用isNaN

submitBtn.onclick = function(){

    var name = document.getElementById('name').value;
    var weight = document.getElementById('weight').value;
    var pound = weight * 2.20462;

    //Check that the value is a number
    if(isNaN(weight)){
       alert("Please enter a number");
    }
}

Js条件声明不起作用

2 个答案: