How to Double Jump

--https://youtu.be/z0CfDQ9zy0o
local UserInputService = game:GetService("UserInputService")
local Players = game:GetService("Players")

local player = Players.LocalPlayer
local character = player.Character or player.CharacterAdded:Wait()
local humanoid = character:WaitForChild("Humanoid")
local rootPart = character:WaitForChild("HumanoidRootPart")

local jumpHeight = 100
local canDoubleJump = false
local hasDoubleJumped = false

humanoid.StateChanged:Connect(function(_, newState)
    if newState == Enum.HumanoidStateType.Landed then
        canDoubleJump = false
        hasDoubleJumped = false
    end
end)

UserInputService.InputBegan:Connect(function(input, gameProcessed)
    if gameProcessed then return end

    if input.KeyCode == Enum.KeyCode.Space then
        if humanoid:GetState() == Enum.HumanoidStateType.Freefall and canDoubleJump and not hasDoubleJumped then
            hasDoubleJumped = true
            rootPart.Velocity = Vector3.new(rootPart.Velocity.X, jumpHeight, rootPart.Velocity.Z)
        elseif humanoid:GetState() ~= Enum.HumanoidStateType.Freefall then
            canDoubleJump = true
        end
    end
end)