update textarea height and refocus when attaching files

also fix extra newline when pasting image into textarea

app/assets/javascripts/dropzone_input.js

@@ -130,13 +130,15 @@ window.DropzoneInput = (function() {
       var afterSelection, beforeSelection, caretEnd, caretStart, textEnd;
       var formattedText = text;
       if (shouldPad) formattedText += "\n\n";
-      caretStart = $(child)[0].selectionStart;
-      caretEnd = $(child)[0].selectionEnd;
+      const textarea = child.get(0);
+      caretStart = textarea.selectionStart;
+      caretEnd = textarea.selectionEnd;
       textEnd = $(child).val().length;
       beforeSelection = $(child).val().substring(0, caretStart);
       afterSelection = $(child).val().substring(caretEnd, textEnd);
       $(child).val(beforeSelection + formattedText + afterSelection);
-      child.get(0).setSelectionRange(caretStart + formattedText.length, caretEnd + formattedText.length);
+      textarea.setSelectionRange(caretStart + formattedText.length, caretEnd + formattedText.length);
+      textarea.style.height = `${textarea.scrollHeight}px`;
       return form_textarea.trigger("input");
     };
     getFilename = function(e) {
@@ -180,7 +182,7 @@ window.DropzoneInput = (function() {
     };
     insertToTextArea = function(filename, url) {
       return $(child).val(function(index, val) {
-        return val.replace("{{" + filename + "}}", url + "\n");
+        return val.replace("{{" + filename + "}}", url);
       });
     };
     appendToTextArea = function(url) {
@@ -215,6 +217,7 @@ window.DropzoneInput = (function() {
     form.find(".markdown-selector").click(function(e) {
       e.preventDefault();
       $(this).closest('.gfm-form').find('.div-dropzone').click();
+      form_textarea.focus();
     });
   }

changelogs/unreleased/30008-textarea-focus.yml

+---
+title: refocus textarea after attaching a file
+merge_request:
+author: