jQuery to Show Image Preview after Validating Image Size and Type Before Upload in Asp.net

Introduction: In this article I have explained How to validate image size and type of the file using jquery before actually uploading on server. Image preview will also be shown if image is of specified size and type.

validate image type and size and show preview using jquery in asp.net

Description: It is very common requirement while working on asp.net project to upload image files e.g. jpg, jpeg, png, bmp, gif etc.  I got the same requirement where user can upload images. But I have to restrict user to upload only certain type of imagesand of up to specified size.

Actually this can be done both server side and client side. But to check the file type or size of file at server size through code, file must be first uploaded into server memory which is time consuming if the size of the file is large. So it will definitely degrade the performance of our application. To overcome this problem we can validate file type and size at client side using jQuery before actually uploading the image.

Implementation: Let’s create a sample page to demonstrate the concept

HTML Source

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <style type="text/css">
        .error {
            background-color: #d9534f;
            font-weight: 300;
            font-size: 12px;
            padding: 3px 6px 3px 6px;
            color: #fff;
            text-align: center;
            white-space: nowrap;
    <script src="http://code.jquery.com/jquery-1.11.3.js" type="text/javascript"></script>
    <script type="text/javascript">
        //Validate image size before upload
        function validateTypeAndSize(uploadCtrl) {
            // Get uploaded file extension
            var extension = $(uploadCtrl).val().split('.').pop().toLowerCase();
            // Create array with the files extensions that we wish to upload
            var validFileExtensions = ['jpeg', 'jpg', 'png', 'bmp'];
            //Check file extension in the array.if -1 that means the file extension is not in the list.
            if ($.inArray(extension, validFileExtensions) == -1) {
                $('#spnMessage').text("Sorry!! Upload only jpg, jpeg, png, bmp image").show();
                // Clear fileuload control selected file
                //Disable Submit Button
                $('#btnSubmit').prop('disabled', true);
                //Clear Image preview
                $('#imgPreview').prop('src', '');
            else {
                // Check and restrict the file size to 32 KB.
                if ($(uploadCtrl).get(0).files[0].size > (32768)) {
                    $('#spnMessage').text("Sorry!! Max allowed image size is 32 kb").show();
                    // Clear fileuload control selected file
                    //Disable Submit Button
                    $('#btnSubmit').prop('disabled', true);
                    //Clear Image preview
                    $('#imgPreview').prop('src', '');
                else {
                    //Clear and Hide message span
                    //Enable Submit Button
                    $('#btnSubmit').prop('disabled', false);
                    //Preview Image if valid
        //Preview image before upload
        function previewImage(input) {
            if (input.files && input.files[0]) {
                var reader = new FileReader();
                reader.onload = function (e) {
                    .attr('src', e.target.result)
    <form id="form1" runat="server">
        <div style="text-align:center">
            <asp:Image ID="imgPreview" Height="150px" Width="200px" runat="server" ClientIDMode="Static" /><br />
            <asp:FileUpload ID="FileUpload1" runat="server" onchange="validateTypeAndSize(this)" /><br />
            <br />
            <asp:Button ID="btnSubmit" runat="server" Text="Submit" Enabled="false" ClientIDMode="Static" /><p>
            <span id="spnMessage" class="error" style="display: none;"></span></p>

Explanation:  User can now upload file of jpg, jpeg, png, gif, bmp type and up to 32 kb size. If user selects any other file or large file than the specified limit then appropriate message will be displayed to user and submit button will be disabled. When a valid file of up to specified size is uploaded then submit button will be enabled and image preview will be shown.

Note: I have restricted user to upload up to 32kb file. If you want to restrict the file size to 2 mb then replace 32768 with 1024*1024*2 in above jquery script.

Now over to you:
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