Comparing two numbers from a form in JavaScript

Question

When i try to compare different numbers, the numbers change but the text part remains the same. This only happens with greater/lesser, and not with NaN or equal case.

Here's my code:

function check() {
    var a = document.getElementById("a").value;
    var b = document.getElementById("b").value;
    
    if (isNaN(a) || isNaN(b) === true) {
        document.getElementById("result").innerHTML = "It's not a number";
    } else {
        if (a > b) {
            document.getElementById("result").innerHTML = "Number " + a + " is greater than number " + b;
        } else if (a == b) {
            document.getElementById("result").innerHTML = "number " + a + " is equal to number " + b;
        } else if (a < b) {
            document.getElementById("result").innerHTML = "number " + a + " is lesser than  number " + b;
        }
    }
}

body {
    background-color: black;
    color: white;
    font-size: 28px;
}

<!DOCTYPE HTML>
<html lang="pl">
    
<head>
    <meta charset="utf-8">
    <title>Check the value of a number compared to the second number</title>
    <script type="text/javascript" src="sprawdzanie.js"></script>
    <link href="style.css" rel="stylesheet">
</head>

<body>

    <input id="a" type="text">
    <input id="b" type="text">
    <input value="Check" type="submit" onclick="check()">
    


    <div id="result"></div>

</body>
    
    
</html>

Please include the code directly in your question.

Felix Kling
– Felix Kling

2018-06-12 17:53:39 +00:00
Commented Jun 12, 2018 at 17:53 — Felix Kling
– Felix Kling, Commented Jun 12, 2018 at 17:53

APerson · Accepted Answer · 2018-06-12 17:55:41Z

1

The values a and b are both strings. If you want to compare them like numbers, use parseInt() or parseFloat() on them before you perform the comparison.

So, before the if statement:

a = parseInt(a);
b = parseInt(b);

answered Jun 12, 2018 at 17:55

APerson

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2 Comments

RKJ Over a year ago

Thanks, any idea why it is buggy with strings ?

APerson Over a year ago

@RKJ The way strings are compared is different from the way numbers are compared; strings are compared character-by-character, which is wrong for numbers if the numbers are of different lengths.

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