Oleksandr Syvyi
--- a/core/modules/file/js/file.js
+++ b/core/modules/file/js/file.js
       $(once('fileValidate', $context.find(selector))).on(
         'change.fileValidate',
         { extensions: elements[selector] },
-          Drupal.file.validateExtension,
--- a/core/modules/file/js/file.js
+++ b/core/modules/file/js/file.js
-     * Client-side file input validation of file extensions.
+    * Client-side file input validation of file extensions and file size.
    *
-     * @name Drupal.file.validateExtension
+    * @name Drupal.file.validateExtensionAndSize
    *
    * @param {jQuery.Event} event
    *   The event triggered. For example `change.fileValidate`.
    */
-    validateExtension(event) {
+   validateExtensionAndSize(event) {
     event.preventDefault();
+     const file = this.files[0];
+
+     // Formats bytes to human friendly unit.
+     function humanFileSize(size) {
--- a/core/modules/file/js/file.js
+++ b/core/modules/file/js/file.js
         event.stopImmediatePropagation();
       }
     }
+
+     // Validate filesize.
+     if (file.size > drupalSettings.file.max_size) {