Question

How can I ensure that at least one field has a selected file using jQuery? Here is my form:

<form action="b.php">
    <input type="file" name="file[]">
    <input type="file" name="file[]">
    <input type="file" name="file[]">
    <input type="file" name="file[]">
    <input type="submit" value="Value">
</form>

Answer 1

To achieve this you can use map() to build an array of all the valid file input elements. You can then check if this array has any elements in it. If it does, then at least one input was valid, if it was empty then nothing has been chosen. Try this:

var validFields = $('input[type="file"]').map(function() {
    if ($(this).val() != "") {
        return $(this);
    }
}).get();    

if (validFields.length) {
    console.log("Form is valid");
} else {
    console.log("Form is not valid");
}

Example fiddle