Javascript validation function always replying invalid

Question

I have done everything correct but still, for all values the function is display "Invalid" only. Can someone tell me where is the problem ?

<html>
<head>
<script>
function alpha()
{ 
var x = document.getElementById('input1'); 
var y = x.value;
var z = isNaN(y);
if(z<1 || z>10){console.log("Invalid");} else {console.log("valid");}
}
</script>
</head>

<body> 
<button id="but1" onmouseover="alpha()" style="background:blue;">Click Me</button> 
<p id=para1> Hello! This is paragraph One! </p> 
<input type=text id=input1 > 
</body> 
</html>

Thanks in advance, and sorry for asking silly question! But, I cant find where code is getting wrong!

The returned value of isNaN is not a number but a boolean. — t.niese
– t.niese, Commented Feb 6, 2015 at 22:25

score 2 · Accepted Answer · 2015-02-06 22:44:14Z

2

isNaN returns a boolean and your comparing it to numbers. you'll want to compare x to your range.

if(z || x<1 || x>10)

Here is how I would clean up your code a bit

function alpha(){ 

    //name your variables something meaningful
    var userInputField = document.getElementById('input1');  

    //using parse int tells yourself and future programmers you want an int
    //it also gives you NaN if it's not a number so you don't have to check yourself
    //the 10 is the radix you want to convert to
    var userInputedValue = parseInt(x.value,10); 
    //check explicitly for NaN will save you some headaches
    if(userInputedValue === NaN || userInputedValue<1 || userInputedValue>10){
        console.log("Invalid");
    } else { 
         console.log("valid");
    }
}

edited Feb 6, 2015 at 22:44

answered Feb 6, 2015 at 22:25

user2033671

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4 Comments

zerkms Over a year ago

You also need parseFloat or parseInt. x is not a number but an element as well.

t.niese Over a year ago

@zerkms while it is definitely better to use the correct type, wouldn't x be implicitly converted to a number when compared that way?

user2033671 Over a year ago

@t.niese if x is a number isNaN(x) would return false, since x is not not a number

user2033671 Over a year ago

@t.niese no worries. double negatives are always a pain

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