How to make file attachment optional?

Question

$sjb_attach_resume = '<div class="col-md-3 col-xs-12">'
        . '<label for="applicant_resume">' . apply_filters('sjb_resume_label', __('Attach Resume', 'simple-job-board')) . '<span class="sjb-required required">*</span></label>'
        . '</div>'
        . '<div class="col-md-9 col-xs-12">
                            <div class="form-group">'
        . '<input type="file" name="applicant_resume" id="applicant-resume" class="sjb-attachment form-control "' . apply_filters('sjb_resume_required', 'required="required"') . '>'
        . '<span class="sjb-invalid-attachment validity-note" id="file-error-message"></span>'
        . '</div>'
        . '</div>'
        . '<div class="clearfix"></div>';
echo apply_filters('sjb_attach_resume', $sjb_attach_resume);

Answer 1

I assume you didn't write the code, since you're asking this. Honestly and respectfully you should learn the basics before playing around with file uploads etc. as it can be a major security risk if not handled properly.

As for your question, you can remove the required-attribute completely from the file input:

$sjb_attach_resume = '<div class="col-md-3 col-xs-12">'
        . '<label for="applicant_resume">' . apply_filters('sjb_resume_label', __('Attach Resume', 'simple-job-board')) . '<span class="sjb-required required">*</span></label>'
        . '</div>'
        . '<div class="col-md-9 col-xs-12">
                            <div class="form-group">'
        . '<input type="file" name="applicant_resume" id="applicant-resume" class="sjb-attachment form-control ">'
        . '<span class="sjb-invalid-attachment validity-note" id="file-error-message"></span>'
        . '</div>'
        . '</div>'
        . '<div class="clearfix"></div>';
echo apply_filters('sjb_attach_resume', $sjb_attach_resume);

...or remove it by modifying the filter applied, by adding a code snippet to your theme's functions.php file:

add_filter( 'sjb_resume_required', '__return_empty_string' );