JS条件语句不起作用

Question

在提交时检查weight变量上的非数字输入时，我的if语句似乎不起作用。 为什么是这样？

   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);
    }
   }

它在JsFiddle链接中

Answer 1

您的代码中存在多个问题：

• 您尝试拨打.onclick上submitBtn ，这是不确定的。
• 您尝试调用.isNan()这应该是.isNaN()
• 您无需关闭传递给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");
    }
}

的jsfiddle

Answer 2

您可能应该使用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");
    }
}