Avoid creating new Array object per each comparison

Benchmark.ips do |x|
  arr = [:js]

  x.report('==') { arr == [:js] }
  x.report('length') { (arr.length == 0) && (arr[0] == :js) }
  x.report('one?') { arr.one? && (arr[0] == :js) }

  x.compare!
end

Warming up --------------------------------------
                  ==   731.426k i/100ms
              length     1.967M i/100ms
                one?     1.440M i/100ms
Calculating -------------------------------------
                  ==      7.291M (± 0.8%) i/s -     36.571M in   5.016130s
              length     19.633M (± 0.8%) i/s -     98.356M in   5.010104s
                one?     14.387M (± 0.8%) i/s -     71.998M in   5.004721s

Comparison:
              length: 19632843.5 i/s
                one?: 14386784.0 i/s - 1.36x  (± 0.00) slower
                  ==:  7291274.5 i/s - 2.69x  (± 0.00) slower

Author: amatsuda

actionview/lib/action_view/lookup_context.rb

@@ -267,7 +267,7 @@ def formats=(values)
           raise ArgumentError, "Invalid formats: #{invalid_values.map(&:inspect).join(", ")}"
         end
 
-        if values == [:js]
+        if (values.length == 1) && (values[0] == :js)
           values << :html
           @html_fallback_for_js = true
         end