How to check value length with using Javascript?

Question

Hello everyone I would like to ask how to check value's length from textbox ?

Here is my code :

@*<script>
    function validateForm() {
        var x = document.forms["frm"]["txtCardNumber"].value;
        if (x == null || x == "" ) {
            alert("First name must be filled out");
            return false;
        }
    }
</script>*@

When I run my script yeap I got alert message but I'm trying to add property which control the texbox' input length.

Answer 1

You could use x.length to get the length of the string:

if (x.length < 5) {
    alert('please enter at least 5 characters');
    return false;
}

Also I would recommend you using the document.getElementById method instead of document.forms["frm"]["txtCardNumber"].

So if you have an input field:

<input type="text" id="txtCardNumber" name="txtCardNumber" />

you could retrieve its value from the id:

var x = document.getElementById['txtCardNumber'].value;

Answer 2

Still more better script would be:

<input type="text" name="txtCardNumber" id="txtCardNumber" />

And in the script:

if (document.getElementById(txtCardNumber).value.length < 5) {
    alert('please enter at least 5 characters');
    return false;
}