gsc-writer

GSC Writer — IW4/MW2 (CoD4 engine)

You are writing GSC for IW4 (Call of Duty: Modern Warfare 2, 2009). IW4 uses an older GSC dialect that is NOT JavaScript, NOT Python, NOT C#, and NOT BO3 GSC. If you assume it works like any of those languages, you will produce broken scripts.

The linter will catch your mistakes. Your job is to not make them in the first place.

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Mandatory Workflow — Do This Every Time

Before Writing (non-negotiable)

1. If editing an existing file — run gsc_outline first. Understand what functions exist before touching anything.
2. For every function you plan to call — run gsc_lookup to verify the exact signature.
3. For any pattern you are unsure about — run gsc_anti_patterns with a relevant keyword (e.g. query="push", query="null", query="object").
4. For scaffolding — run gsc_template with list=true to find existing templates before writing from scratch.

While Writing

5. Follow every rule in the Critical Rules section below. Read them before writing.

After Writing

6. Run gsc_lint on every file you touched — zero tolerance for errors. Re-write until clean.
7. Run gsc_fix if the linter reports fixable issues, then lint again.
8. Never claim a file is done unless gsc_lint returns zero errors.

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Pre-Flight Checklist (Before Writing Each Function)

Answer YES to all before writing a single line:

• Did I run gsc_outline on the file I am editing? (existing files only)
• Did I run gsc_lookup for every built-in function I plan to use?
• Did I check gsc_anti_patterns for any pattern I am unsure about?
• Does my function signature have NO function keyword?
• Do I have ZERO var, let, or const in my code?
• Do all my array loops use indexed for with .size?
• Does every infinite loop have a wait or waittill inside it?
• Does every waittill, notify, and endon have an entity prefix?
• Am I using isDefined() instead of null checks?
• Am I using spawnstruct() instead of {} object literals?

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Critical Rules — IW4 GSC Dialect

NEVER List — The Linter Will Reject These as Errors

Rule	WRONG	RIGHT
No function keyword	function init() {}	init() {}
No var/let/const	var x = 5;	x = 5;
No .push()	arr.push(item)	arr[arr.size] = item;
No .length	arr.length	arr.size
No ===/!==	x === 5	x == 5
No ternary ?:	x > 0 ? a : b	if (x > 0) ... else ...
No arrow functions	(x) => x + 1	write a named function
No {key: val} objects	obj = {x: 1}	obj = spawnstruct(); obj.x = 1;
No null	if (x == null)	if (!isDefined(x))
No Math.*/parseInt	Math.floor(x)	int(x)
No template literals	`hi ${name}`	"hi " + name
No new	new Object()	spawnstruct()
No this.	this.health	self.health
No for...of/forEach	for (p of players)	for (i=0; i<players.size; i++)
No .concat()/.join()	"a".concat("b")	"a" + "b"

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Entity Rules

• self = the entity the current function is called on. Never use this.
• level = shared global game state. Common fields: level.players, level.teamBased, level.time.
• game = game mode state. Access with game["key"].
• Entity method calls use a space, not dot: entity methodName(args) — NOT entity.methodName(args).
• Always check before accessing: if (isDefined(player.customProp)) before using any custom property.

Event System Rules

// ALWAYS prefix waittill/notify/endon with an entity:
self waittill("damage", amount, attacker);  // correct
waittill("damage");                          // WRONG — missing entity

// ALWAYS include wait in infinite loops:
for (;;)
{
    doWork();
    wait 0.05;   // required — server freezes without this
}

// Spawn threads for async work:
level thread watchGame();   // non-blocking — correct
watchGame();                // blocks the calling function

Array Rules

// Append to array:
arr[arr.size] = newItem;   // correct
arr.push(newItem);         // WRONG

// Get length:
count = arr.size;          // correct
count = arr.length;        // WRONG

// Iterate:
for (i = 0; i < arr.size; i++)   // correct
for (item of arr)                 // WRONG

Object Rules

// Create objects:
data = spawnstruct();   // correct
data.x = 1;
data.y = 2;

data = { x: 1, y: 2 }; // WRONG — invalid syntax

// Null checks:
if (!isDefined(x)) {}   // correct
if (x == null) {}       // WRONG — null does not exist

// Remove a property:
obj.prop = undefined;   // correct
delete obj.prop;        // WRONG — no delete operator

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File Structure

A valid IW4 GSC file:

// Optional includes
#include maps\mp\gametypes\_hud_util;

// Entry point — no function keyword
init()
{
    level thread onPlayerConnect();
}

onPlayerConnect()
{
    for (;;)
    {
        level waittill("connected", player);
        player thread onPlayerSpawn();
    }
}

onPlayerSpawn()
{
    self endon("disconnect");
    for (;;)
    {
        self waittill("spawned_player");
        // self is the player entity here
    }
}

Key points:

• No function keyword anywhere
• Opening { on a new line (IW4 convention)
• Infinite loops always have wait or waittill
• Threads begin with self endon("disconnect")

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Quick Validation Checklist

Before calling a file done, scan for:

• Zero function keywords in definitions
• Zero var/let/const
• Zero .push()/.pop()/.length
• Zero ===/!==
• Zero null literals
• Zero this. references
• Every waittill/notify/endon has an entity prefix
• Every infinite loop has wait or waittill inside
• gsc_lint returns zero errors