Validations before deleting files. Use filepredelete event to do your validations and return an abort status as mentioned in the event manipulation documentation. For example raise a confirmation dialog for delete. Return true (or any valid value/object other than false or null or empty string) if you wish to abort the delete process. You can do further operations if you want on this by trapping the filecustomerror event. Your filecustomerror event, can receive data that you return from these other events.

Code

<div class="file-loading">
    <input id="input-707" name="kartik-input-707[]" type="file" multiple>
</div>

<script>
$(document).ready(function() {
    $("#input-707").fileinput({
        uploadUrl: "/file-upload-batch/1",
        uploadAsync: false,
        minFileCount: 2,
        maxFileCount: 5,
        overwriteInitial: false,
        initialPreview: [
            "<img class='file-preview-image kv-preview-data' src='http://lorempixel.com/800/460/nature/1'>",
            "<img class='file-preview-image kv-preview-data' src='http://lorempixel.com/800/460/nature/2'>",
            "<img class='file-preview-image kv-preview-data' src='http://lorempixel.com/800/460/nature/3'>",
        ],
        initialPreviewConfig: [
            {caption: "Food-1.jpg", description: 'This is a representative placeholder description for this image.', size: 329892, url: "/site/file-delete", key: 1},
            {caption: "Food-2.jpg", description: 'This is a representative placeholder description for this image.', size: 872378, url: "/site/file-delete", key: 2}, 
            {caption: "Food-3.jpg", description: 'This is a representative placeholder description for this image.', size: 632762, url: "/site/file-delete", key: 3}, 
        ],
        uploadExtraData: {
            img_key: "1000",
            img_keywords: "happy, nature",
        }
    });
    $("#input-707").on("filepredelete", function(jqXHR) {
        var abort = true;
        if (confirm("Are you sure you want to delete this image?")) {
            abort = false;
        }
        return abort; // you can also send any data/object that you can receive on `filecustomerror` event
    });
});
</script>