Question

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Validate that a string is a positive integer

So I want to check a form field if it’s empty and to allow it to has only positive numeric numbers, no spaces or letters. So far I succeed the first part to check if the field is empty with the following code:

function validate(form) {
    var elements = form.elements;

    if (form.qty.value == "") {
        alert("Please enter the field");
        document.forms[0].qty.focus()
        document.forms[0].qty.select()
        return false;
    }

    return true;
}

Somewhere in the form:

<form action="addtocart.php" method ="post" onsubmit="return validate(this);" /> …

But now I want to allow only numbers as well as to check if the field is empty. I have found some scripts but I don’t know how to merge the code into one valid script.

Answer 1

if (Number(form.qty.value) > 0) {
    // Only executes if value is a positive number.
}

Note that if the value is an empty string the statement will not return true. The same goes for null, NaN (obviously) and undefined. String representations of numbers are transformed into their numeric counterparts.