Module B1 · Lua basics

Choosing a runtime: Lua, JavaScript, or C#

This is a decision lesson, not a heavy build. FiveM does not run one language. It runs three: Lua 5.4, JavaScript on Node, and C# on .NET. Most of what you will read, fork, and ship is Lua, which is why this course teaches Lua. But you should know the other two exist, how the manifest declares them, and the narrow cases where reaching past Lua is the right call. The build at the end is small on purpose: one JavaScript server script printing alongside a Lua one, so you see with your own eyes that they coexist in the same resource.

You'll build: A two-file resource that proves Lua and JavaScript run side by side: a Lua server script and a JavaScript server script that both print on start.
Time: ~16 minutes
You need: A local FiveM practice setup you can restart, and a text editor. You do not need Node or the .NET SDK installed for this lesson. FiveM ships the JavaScript runtime inside the server.
You'll learn: What the three FiveM runtimes are, how each is declared in fxmanifest, when to reach for each, and why this course stays Lua-first.

BEFORE YOU START

The three runtimes

FiveM exposes the same scripting platform through three language runtimes. They all see the same natives, the same events, the same resource model. The difference is the language you write and the engine that runs it.

Symptom	Fix
`Only the Lua line prints; the JavaScript line never appears`	The server.js server_script line is missing from fxmanifest.lua, or the file is named server.js but the manifest points at a different name. Add server_script 'server.js' and confirm the filename matches exactly.
`Could not find dependency node for resource, or the JS script fails to load on an older server`	The node_version pin is missing or set to a version the server cannot provide. Add node_version '22' to the manifest and update the server artifact if it predates Node 22 support.
`Adding lua54 'yes' produces a warning or has no effect`	That directive was deprecated in June 2025 and is ignored. Lua 5.4 is the only Lua runtime now. Delete the line; it does nothing.
`Expecting C# to run from a .cs file in server_script`	C# does not run from source. You compile the .cs files with the .NET SDK into a .net.dll first, then declare that dll in the manifest. There is no source-level C# script directive.
`Nothing prints at all for either language`	The resource is not started. Confirm ensure qu_runtimes is in server.cfg, then run restart qu_runtimes and read the txAdmin Live Console at the moment of restart, since both lines fire on start, not on a command.

Choosing a runtime: Lua, JavaScript, or C#

The three runtimes

Lua 5.4: the default this course teaches

JavaScript on Node: for NUI-heavy work and JS developers

C# on .NET: compiled, for large or enterprise systems

Build it

Make the resource folder

Create the files

Write fxmanifest.lua

Write the Lua script

Write the JavaScript script

Start and test it

How it works

The two server_script lines

The node_version pin

print versus console.log

When you reach for each runtime

Common mistakes

What you can do now

Try it yourself