How do I make a double tap for script.byte keys?

Alright, so I made a dash script. But instead of it just being one key I want it to be w + w. You would just tap w twice in less than 1 second. I don't know how to do that. How do I make it so that it's a double-tap thingy?

local player = game.Players.LocalPlayer
repeat wait() until player.Character.Humanoid
local humanoid = player.Character.Humanoid
local mouse = player:GetMouse()

local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/asset/?id=" 

mouse.KeyDown:connect(function(key)
    if string.byte(key) == ??? then 
        local playAnimation = humanoid:LoadAnimation(anim)
        playAnimation:Play()
        script.Sound:Play()
        player.Character.HumanoidRootPart.Velocity = player.Character.HumanoidRootPart.CFrame.lookVector * 100
        wait(2.0)
    end
    wait(10)
end)