Re-define react event handler methods using arrow functions

arrow_function_event_handlers.rb

#!/usr/bin/env ruby

#
# Given some react components written as ES6 classes, this converts any event handler methods from "normal"
# class methods to be arrow functions, assigned to static variables in the class. That way the method is
# always bound to "this".
#

file_paths = ARGV

BIND_REGEXP = /this\.(\w+)\.bind\(this\)/
CALL_PROP_REGEXP = /=\{\s*\((.*?)\)\s*=>\s*\{?\s*(\w+)\(\1\)\s*\}?\s*\}/
ANON_FUNC_REGEXP = /=\{\s*\((.*?)\)\s*=>\s*\{?\s*this\.(\w+)\(\1\)\s*\}?\s*\}/

def replace_bind_with_arrow(contents)
  contents.scan(BIND_REGEXP).uniq.each do |(callback_fn)|
    method_found = !!contents.sub!(/#{callback_fn}\s*\((.*?)\)\s*\{/, "#{callback_fn} = (\\1) => {")
    if method_found
      contents.gsub!("this.#{callback_fn}.bind(this)", "this.#{callback_fn}")
    else
      class_name = contents[/class (\w+)/, 1]
      puts "Could not find definition of #{class_name}.#{callback_fn}() to rewrite using an arrow function"
    end
  end
  contents
end

def call_prop_directly(contents)
  contents.scan(CALL_PROP_REGEXP).uniq.each do |(prop_fn)|
    contents.gsub!(/=\{\s*\((.*?)\)\s*=>\s*\{?\s*#{prop_fn}\(\1\)\s*\}?\s*\}/, "={#{prop_fn}}")
  end
  contents
end

def replace_anon_funcs_with_arrow(contents)
  contents.scan(ANON_FUNC_REGEXP).uniq.each do |(_args, anon_fn)|
    method_found = !!contents.sub!(/#{anon_fn}\s*\((.*?)\)\s*\{/, "#{anon_fn} = (\\1) => {")
    if method_found
      contents.gsub!(/=\{\s*\((.*?)\)\s*=>\s*\{?\s*this\.#{anon_fn}\(\1\)\s*\}?\s*\}/, "={this.#{anon_fn}}")
    else
      class_name = contents[/class (\w+)/, 1]
      puts "Could not find definition of #{class_name}.#{anon_fn}() to rewrite using an arrow function"
    end
  end
  contents
end

file_paths.each do |path|
  throw "Invalid path #{path}" unless File.exist?(path)
  contents = File.read(path)
  updated_contents = replace_anon_funcs_with_arrow(call_prop_directly(replace_bind_with_arrow(contents)))
  File.write(path, updated_contents)
end