Lua oop middleclass spawn enemies with random x coordinate

I make a game with lua/LÖVE and i use the middleclass library for OOP, but i have a problem, my game is a space shooter game with a base class "entity" a subclass "player" and "meteor" (enemy that fall from the top of the screen with a random x coordinate) but i don't know how to make the random spawn system for the meteor (a random x coordinate).

Entity = class('Entity')

function Entity:initialize(x, y, width, height, image)
  self.x = x
  self.y = y
  self.width = width
  self.height = height
  self.image = image
end

function Entity:draw()
  love.graphics.draw(self.image, self.x, self.y)

    end

meteor.lua = http://ift.tt/2s3Dkpb gameState.lua = http://ift.tt/2sD1iVi

(the game file)

Everytimes that i launch the game, the x coordinate of the meteor object is the same, i want to spawn one meteor with a random x coordinate every 2 seconds, but i don't know how to do that. I think that i've made something wrong but i don't know. :/

After that i would like also to delete the object when it is outside of the screen. I know how to do that without oop but with oop i'm stuck...

Thanks you in advance !