Roblox Hot-Reloader for plugins!

This package hot-reloads modules in roblox studio with an isolated environment and avoids module caching.

This module requires access to loadstring and it's recommended to be used only in Plugins. For hot-reloading in games, check Rewire

This package is used in UI Labs

How to use:

Loading a module:

Let's see how you can load a module

First let's create an Environment where all the modules will live

local HMR = require("hmr")
local Environment = HMR.Environment

local env = Environment.new()

Now that we have an environment where our required modules can live, rather than using require(...) we load a module using env:LoadDependency(module). This will return a Promise that resolves with the result of the module, or rejects if the module failed to run.

Note that this will also use LoadDependency recursively on any require call used inside of the module.

local env = Environment.new()

local module = ...
local dependency = env:LoadDependency(module)
local dependencyReturn = dependency:expect()

You can require more modules in the Environment by calling env:LoadDependency() again. Modules that have already been loaded (required) by either you or automatically will return the cached result. If a module is in the proccess of being required it will return the same promise

local module = ...

local dep = env:LoadDependency(module):expect()
local dep2 = env:LoadDependency(module):expect() --returns the cached result

print(dep == dep2) --true

Accessing the _G table

Modules that are required in this environment will access a separated _G table instead of the real one. You can access this table in env.Shared

Modifying globals

HMR environment replaces the globals script, require and _G in the modules to work, if you want to modify the globals with your custom values you can do this by calling env:InjectGlobal(key, value).

you cant modify the globals that HMR already replaces (script, require, _G)

local env = Environment.new()

env:InjectGlobal("print", function(...)
   print("printed from environment:", ...)
end)
env:InjectGlobal("customglobal", 10)



------ [[ in the required module ]] ------

print("hello world") -- printed from environment: hello world

local injected = customglobal --10
local injected = getfenv()["customglobal"] --10

env:InjectGlobal() will call env:EnableGlobalInjection() if it hasnt been enabled, however, if you require a module while global injections arent enabled, these changes wont work for that module, so, if you plan to replace globals at some point after you already loaded a module, you should call env:EnableGlobalInjection() before

Listening for changes

HMR environment listens for changes in the module scripts that have been required. you can check when any of the required modules have been changed using the signal env.OnDependencyChanged. This can be used to reload the modules when any of the modules change. You can registry a module to listen by calling env:ListenDependency(module). This will not load the module, it only listens for env.OnDependencyChanged

local env = Environment.new()

env.OnDependencyChanged:Connect(function(module)
    print("Module", module.Name, "has changed")
end)

Reloading the modules

When you want to reload these modules again (by listening env.OnDependencyChanged for example) you need to create a new Environment and Destroy() the old one.

Calling env:Destroy() will not pause or cancel any code running in the required modules and will still receive env:LoadDependency() calls.

This will only disconnect changes for env.OnDependencyChanged, so make sure any running code in the modules gets cleaned.

local connection = nil
local env = nil
local module = ...

function LoadModule()
    if connnection then
        connection:Disconnect()
    end
    if env then
        env:Destroy()
    end

    env = Environment.new()
    env:LoadDependency(module)

    connection = env.OnDependencyChanged:Connect(function()
        LoadModule()
    end)
end

LoadModule()

Hook on destroyed

You can use env:HookOnDestroyed(callback) to call a callback before the environment gets destroyed. Note that this is a callback and not a connection, so if you call it twice, only the last callback will be invoked

Using the Hot-Reloader

HMR also exports a HotReloader that requires a module and automatically listens for env.OnDependencyChanged, managing and destroying the Environment for you. When the HotReloader is reloaded HotReloader.OnReloadStarted connection is fired HMR

This is used in UI Labs to automatically hot-reload stories

local HMR = require("hmr")
local HotReloader = HMR.HotReloader

local reloader = HotReloader.new(module) -- Entry module is required

reloader.OnReloadStarted:Connect(function(result)
    result:andThen(function(val)
        print("Reloaded", val)
    end)
end)

-- Use this to start the hot-reloader, you can also call this to force it to reload again
local dependency = reloader:Reload()

Managing the Environment in the Hot-Reloader

The Hot-Reloader has HotReloader:BeforeReload(callback), this will invoke the callback function before loading the module but after creating a new environment. Useful for setting up the environment before requiring the modules, this is a callback and not a connection, delaying this callback will delay the reloading and can cause unexpected results

local HMR = require("hmr")
local HotReloader = HMR.HotReloader

local reloader = HotReloader.new(module) -- Entry module is required

-- This should be called before reloading
reloader:BeforeReload(function(env)
    env:InjectGlobal("print", function(...)
       print("printed from environment:", ...)
    end)
end)

local dependency = reloader:Reload()

Turning off AutoReloading

You can turn off Auto-Reloading with HotReloader.AutoReload, this is true by default, setting it to false will skip env.OnDependencyChanged events. Setting it to false will still accept HotReloader:Reload() calls

local reloader = HotReloader.new(module)

-- No longer listens changes
reloader.AutoReloader = false

reloader:Reload() -- It will still reload the module

-- Listens changes again
reloader.AutoRelaoder = true

Extra

Environment:

• Environment:GetDependencyResult(module) returns the loaded module result if exist without requiring it
• Environment:IsDependency(module) returns if a module is loaded
• Environment.EnvironmentUID unique HttpService GUID for this environment

Hot Reloader:

• HotReloader.Module module passed in HotReloader.new()
• HotReloader.GetEnvironment() returns the current environment.
• HotReloader:Destroy() will destroy the current environment and the reload connections
• HotReloader.OnDependencyChanged fires when env.OnDependencyChanged is fired