Don't use params[:view] directly.

app/helpers/diff_helper.rb

 module DiffHelper
+  def diff_view
+    params[:view] == 'parallel' ? 'parallel' : 'inline'
+  end
+
   def allowed_diff_size
     if diff_hard_limit_enabled?
       Commit::DIFF_HARD_LIMIT_FILES
@@ -137,7 +141,7 @@ module DiffHelper
     # Always use HTML to handle case where JSON diff rendered this button
     params_copy.delete(:format)
 
-    link_to url_for(params_copy), id: "inline-diff-btn", class: (params[:view] != 'parallel' ? 'btn active' : 'btn') do
+    link_to url_for(params_copy), id: "inline-diff-btn", class: (diff_view == 'inline' ? 'btn active' : 'btn') do
       'Inline'
     end
   end
@@ -148,7 +152,7 @@ module DiffHelper
     # Always use HTML to handle case where JSON diff rendered this button
     params_copy.delete(:format)
 
-    link_to url_for(params_copy), id: "parallel-diff-btn", class: (params[:view] == 'parallel' ? 'btn active' : 'btn') do
+    link_to url_for(params_copy), id: "parallel-diff-btn", class: (diff_view == 'parallel' ? 'btn active' : 'btn') do
       'Side-by-side'
     end
   end

app/views/projects/commit/show.html.haml

@@ -3,4 +3,4 @@
 = render "commit_box"
 = render "ci_menu" if @ci_commit
 = render "projects/diffs/diffs", diffs: @diffs, project: @project
-= render "projects/notes/notes_with_form", view: params[:view]
+= render "projects/notes/notes_with_form"

app/views/projects/diffs/_diffs.html.haml

-- if params[:view] == 'parallel'
+- if diff_view == 'parallel'
   - fluid_layout true
 
 - diff_files = safe_diff_files(diffs)

app/views/projects/diffs/_file.html.haml

@@ -33,7 +33,7 @@
     -# Skipp all non non-supported blobs
     - return unless blob.respond_to?('text?')
     - if blob.text?
-      - if params[:view] == 'parallel'
+      - if diff_view == 'parallel'
         = render "projects/diffs/parallel_view", diff_file: diff_file, project: project, blob: blob, index: i
       - else
         = render "projects/diffs/text_file", diff_file: diff_file, index: i
@@ -42,4 +42,3 @@
       = render "projects/diffs/image", diff_file: diff_file, old_file: old_file, file: blob, index: i
     - else
       .nothing-here-block No preview for this file type
-

app/views/projects/notes/_form.html.haml

 = form_for [@project.namespace.becomes(Namespace), @project, @note], remote: true, html: { :'data-type' => 'json', multipart: true, id: nil, class: "new_note js-new-note-form common-note-form gfm-form" }, authenticity_token: true do |f|
-  = hidden_field_tag :view, params[:view]
+  = hidden_field_tag :view, diff_view
   = hidden_field_tag :line_type
   = note_target_fields(@note)
   = f.hidden_field :commit_id

app/views/projects/notes/_notes_with_form.html.haml

@@ -4,7 +4,7 @@
 
 .js-main-target-form
 - if can? current_user, :create_note, @project
-  = render "projects/notes/form", view: params[:view]
+  = render "projects/notes/form", view: diff_view
 
 :javascript
-  window._notes = new Notes("#{namespace_project_notes_path(namespace_id: @project.namespace, target_id: @noteable.id, target_type: @noteable.class.name.underscore)}", #{@notes.map(&:id).to_json}, #{Time.now.to_i}, "#{params[:view]}")
+  window._notes = new Notes("#{namespace_project_notes_path(namespace_id: @project.namespace, target_id: @noteable.id, target_type: @noteable.class.name.underscore)}", #{@notes.map(&:id).to_json}, #{Time.now.to_i}, "#{diff_view}")