Support text/javascript as JavaScript MIME type

Next Rack release (probably 3.1) will include this change:

rack/rack@1bd0f15
sinatra#1857 (comment)

lib/sinatra/base.rb

@@ -1402,7 +1402,13 @@ def mime_type(type, value = nil)
       #   mime_types :js   # => ['application/javascript', 'text/javascript']
       def mime_types(type)
         type = mime_type type
-        type =~ %r{^application/(xml|javascript)$} ? [type, "text/#{$1}"] : [type]
+        if type =~ %r{^application/(xml|javascript)$}
+          [type, "text/#{$1}"]
+        elsif type =~ %r{^text/(xml|javascript)$}
+          [type, "application/#{$1}"]
+        else
+          [type]
+        end
       end
 
       # Define a before filter; runs before all requests within the same

sinatra-contrib/spec/json_spec.rb

@@ -57,7 +57,10 @@ def results_in(obj)
 
   it "accepts shorthands for :content_type" do
     mock_app { get('/') { json({}, :content_type => :js) } }
-    expect(get('/')["Content-Type"]).to eq("application/javascript;charset=utf-8")
+    # Changed to "text/javascript" in Rack >3.0
+    # https://github.com/sinatra/sinatra/pull/1857#issuecomment-1445062212
+    expect(get('/')["Content-Type"])
+      .to eq("application/javascript;charset=utf-8").or eq("text/javascript;charset=utf-8")
   end
 
   it 'calls generate on :encoder if available' do

test/helpers_test.rb

@@ -681,11 +681,13 @@ def status_app(code, &block)
           assert_equal content_type(:foo),    'text/foo;charset=utf-8'
           assert_equal content_type(:xml),    'application/xml;charset=utf-8'
           assert_equal content_type(:xhtml),  'application/xhtml+xml;charset=utf-8'
-          assert_equal content_type(:js),     'application/javascript;charset=utf-8'
           assert_equal content_type(:json),   'application/json'
           assert_equal content_type(:bar),    'application/bar'
           assert_equal content_type(:png),    'image/png'
           assert_equal content_type(:baz),    'application/baz;charset=utf-8'
+          # Changed to "text/javascript" in Rack >3.0
+          # https://github.com/sinatra/sinatra/pull/1857#issuecomment-1445062212
+          assert_match %r{^application|text/javascript;charset=utf-8$}, content_type(:js)
           tests_ran = true
           "done"
         end