class Opal::Nodes::DefinedNode

def compile_defined_gvar(node)
  helper :gvars
  name = node.children[0].to_s[1..-1]
  gvar_temp = scope.new_temp
  if %w[~ !].include? name
    push "(#{gvar_temp} = ", expr(node), ' || true)'
  else
    push "(#{gvar_temp} = $gvars[#{name.inspect}], #{gvar_temp} != null)"
  end
  gvar_temp
end