JS條件語句不起作用

Question

在提交時檢查weight變量上的非數字輸入時，我的if語句似乎不起作用。 為什么是這樣？

   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鏈接中

Answer 1

您的代碼中存在多個問題：

• 您嘗試撥打.onclick上submitBtn ，這是不確定的。
• 您嘗試調用.isNan()這應該是.isNaN()
• 您無需關閉傳遞給alert()函數的字符串：

//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

您可能應該使用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");
    }
}