WordPress Custom Profile Image Ajax Upload

file-upload.css

.upload-thumb {
  display: inline-block;
  width: 120px;
  height: 120px;
  overflow: hidden;
  background: #e2e2e2;
  border: 1px solid #cdcdcd;
  line-height: 120px;
  margin-bottom: 10px;
}
.upload-thumb.cover {
  width: 500px;
}

.file-upload {
  position: relative;
  overflow: hidden;
}

.file-upload input.upload {
  position: absolute;
  top: 0;
  right: 0;
  margin: 0;
  padding: 0;
  font-size: 20px;
  cursor: pointer;
  opacity: 0;
  filter: alpha(opacity=0);
}

file-upload.js

(function($){

	$('input[type=file][data-ajaxed=Y]').on('change', function(event) {

		files = event.target.files;
		var cont = $(this).attr('data-cont');
		var name = $(this).attr('name');

		var data = new FormData();
		$.each(files, function(key, value)
		{
			data.append(key, value);
		});

		data.append('partner_info_post_id', $(this).closest('form').find("#partner_info_post_id").val() );
		data.append('type', $(this).data('type'));

		$(cont).html('<img src="/assets/images/preloader.gif" />');

		$.ajax({
			url: '/wp-admin/admin-ajax.php?action=file_upload&fname='+name, // Url to which the request is send
			type: "POST",             // Type of request to be send, called as method
			data: data, // Data sent to server, a set of key/value pairs (i.e. form fields and values)
			
			dataType: 'json',
			contentType: false,       // The content type used when sending data to the server.
			cache: false,             // To unable request pages to be cached
			processData:false,        // To send DOMDocument or non processed data file it is set to false
			success: function(data)   // A function to be called if request succeeds
			{
				console.log(data);
				if(data.error)
				{
					alert(data.error);
				}
				else
				{
					$(cont).html('<img src="'+data.src+'" style="max-width:100%;" />');
					$('[name='+name+'_aid]').val(data.aid);
				}
			},
			error: function(jqXHR, textStatus, errorThrown)
			{
				// Handle errors here
				console.log('ERRORS: ' + textStatus);
				alert('ERRORS: ' + textStatus);
				$(cont).html('error');
				// STOP LOADING SPINNER
			}
		});
	
	});


})(jQuery);

functions.php

<?php

add_action('wp_ajax_file_upload', 'dg_file_upload_handler' );
function dg_file_upload_handler()
{
    //Get the file
    $f = 0;
    $_FILES[$f] = $_FILES[0];
    
    $user = new WP_User(get_current_user_id());
    $json['status'] = 'error';
  
    //Check if the file is available && the user is logged in
    if (!empty($_FILES[$f]) && $user->ID > 0) {
      
        $json = array();
        require_once(ABSPATH . 'wp-admin/includes/image.php');
        require_once(ABSPATH . 'wp-admin/includes/file.php');
        require_once(ABSPATH . 'wp-admin/includes/media.php');
       
        //Handle the media upload using WordPress helper functions
        $attachment_id = media_handle_upload($f, 0);
        $json['aid']   = $attachment_id;
        
        //If error
        if (is_wp_error($attachment_id)) {
            $json['error'] = "Error.";
        } else {
            //delete current
            $profile_image = get_user_meta($user->ID, 'profile_image', true);
            if ($profile_image) {
                $profile_image = json_decode($profile_image);
                if (isset($profile_image->attachment_id)) {
                    wp_delete_attachment($profile_image->attachment_id, true);
                }
            }
            
            //Generate attachment in the media library
            $attachment_file_path = get_attached_file($attachment_id);
            $data                 = wp_generate_attachment_metadata($attachment_id, $attachment_file_path);
            
            //Get the attachment entry in media library
            $image_full_attributes  = wp_get_attachment_image_src($attachment_id, 'full');
            $image_thumb_attributes = wp_get_attachment_image_src($attachment_id, 'smallthumb');
            
            $arr = array(
                'attachment_id' => $attachment_id,
                'url' => $image_full_attributes[0],
                'thumb' => $image_thumb_attributes[0]
            );
            
            //Save the image in the user metadata
            update_user_meta($user->ID, 'profile_image', json_encode($arr));
            
            $json['src']    = $arr['thumb'];
            $json['status'] = 'ok';
        }
    }
    //Output the json
    die(json_encode($json));
}

upload-form.php

<?php
$user_id      = get_current_user_id();
$profile_img	= @json_decode(get_user_meta($user_id, 'profile_image', true));
$profile_img  = !$profile_img ? '' : $profile_img;
?>
<div class="profile-picture">
  <div class="upload-thumb profile_image">
    <img src="<?php echo $profile_img->thumb; ?>">
  </div>
  <div>
    <div class="file-upload button">
      <span>Upload</span>
      <input data-type="image" type="file" data-ajaxed="Y" data-cont=".profile_image" name="image" class="upload" />
      <input type="hidden" name="image_aid" value="" />
    </div>
  </div>	
</div>

I got the following error in functions.php file:
Fatal error: Uncaught Error: Using $this when not in object context in

This is how I fixed this
LOOK FOR:
add_action('wp_ajax_file_upload', array($this->ajax, 'dg_file_upload_handler' ) );

REPLACE WITH:
add_action('wp_ajax_file_upload', 'dg_file_upload_handler' );

Thanks for the contribution. The gist has been updated.