Luau globals

A table that is shared between all scripts of the same context level. Any value written to _G from one script is visible to every other script at that same context level, which makes it a simple way to share state between scripts.

-- Script A (sets a value)
_G.mySharedValue = "hello from Script A"

Note that relying on `_G` for cross-script communication introduces
ordering dependencies and makes code harder to reason about. Prefer
`Class.ModuleScript` for shared state when possible.

A global variable (not a function) that holds a string containing the current interpreter version.

Throws an error if the provided value is false or nil. If the assertion passes, it returns all values passed to it.

Performs the specified operation of the garbage collector. Note that Roblox's Luau sandbox only allows the count option to be used (the total memory in use by Luau, in kilobytes), as other options can interfere with existing processes. Effectively, this makes LuaGlobals.gcinfo() a superior alternative that should be used instead.

Terminates the last protected function called and outputs message as an error message. If the function containing the error is not called in a protected function such as pcall(), then the script which called the function will terminate. The error function itself never returns and acts like a script error.

The level argument specifies how to get the error position. With level 1 (the default), the error position is where the error function was called. Level 2 points the error to where the function that called error was called; and so on. Passing a level 0 avoids the addition of error position information to the message.

Returns the total memory heap size in kilobytes. The number reflects the current heap consumption from the operating system perspective, which fluctuates over time as garbage collector frees objects.

Returns the current environment in use by the caller, as a dictionary.

• If provided with a function, the environment of the function will be returned.
• If provided with an integer, LuaGlobals.getfenv() will provide the environment of the function at the provided stack level: Level 1 is the function calling LuaGlobals.getfenv(). If stack is 0, LuaGlobals.getfenv() returns the global environment of the current script. When using LuaGlobals.getfenv() to get the current environment of a script, it will return the same table every time within the specific thread.

WARNING: This function allows uncontrolled change of the global/function environment and disables script optimizations. Changes to the environment are not tracked by the script analysis tooling and may result in missing or incorrect warnings. As a replacement, consider using debug.info() instead.

Returns the metatable of the given value t if it has one, otherwise returns nil. If t does have a metatable, and the __metatable metamethod is set, it returns that value instead.

t can be a value of any type, not only a table, and this function doesn't error when t isn't a table. However, it doesn't always return nil for non-table values. Strings and many Roblox types, such as Instance, have locked metatables, so this function returns the string "The metatable is locked" for them. To check whether a value uses a specific metatable, compare the result directly, such as getmetatable(value) == MyClass.

Returns three values: an iterator function, the table t and the number 0. Each time the iterator function is called, it returns the next numerical index-value pair in the table. When used in a generic for-loop, the return values can be used to iterate over each numerical index in the table:

Loads Luau code from a string and returns it as a function.

Unlike standard Lua 5.1, Roblox's Luau cannot load the compiled bytecode using loadstring().

loadstring() is disabled by default. For guidance around enabling it, see ServerScriptService.

WARNING: This method disables certain Luau optimizations on the returned function. Extreme caution should be taken when using LuaGlobals.loadstring(); if your intention is to allow users to run code in your experience, make sure to protect the returned function's environment by using LuaGlobals.getfenv() and LuaGlobals.setfenv().

Creates a blank zero-size userdata with the option for it to have a metatable. If addMetatable is true, an empty metatable is created and assigned to the userdata; you can then retrieve it with LuaGlobals.getmetatable() and populate it with metamethods. If addMetatable is false or omitted, the userdata has no metatable and only serves as a unique identity token.

Unlike host-created userdata (Roblox instances), a newproxy-created userdata always reports "userdata" from both LuaGlobals.type() and typeof(); setting a __type metamethod on it does not change the typeof() result.

-- Create a proxy with a metatable to implement custom tostring
local proxy = newproxy(true)
local mt = getmetatable(proxy)

mt.__tostring = function()
	return "MyProxy"
end

print(tostring(proxy)) --> MyProxy
print(type(proxy)) --> userdata

Returns the first key/value pair in the array. If a lastKey argument was specified then returns the next element in the array based on the key that provided. The order in which the indices are enumerated is not specified, even for numeric indices. To traverse a table in numeric order, use a numerical for loop or ipairs.

The behavior of next is undefined if, during the traversal, you assign any value to a non-existent field in the table. You may, however, modify existing fields. In particular, you may clear existing fields.

Returns an iterator function, the passed table t, and nil, so that the construction will iterate over all key/value pairs of that table when used in a generic for loop:

Calls the function func with the given arguments in protected mode. This means that any error inside func is not propagated; instead, pcall() catches the error and returns a status code. Its first result is the status code (a boolean), which is true if the call succeeds without errors. In such case, pcall() also returns all results from the call, after this first result. In case of any error, pcall() returns false plus the error message.

Receives any number of arguments, and prints their values to the output. print is not intended for formatted output, but only as a quick way to show a value, typically for debugging. For a formatted output, use string.format(). On Roblox, print does not call tostring, but the __tostring metamethod still fires if the table has one.

Checks whether v1 is equal to v2 without invoking the __eq metamethod. The comparison uses primitive equality rules: values of different types are never equal; nil equals only itself; numbers and vectors are compared by value; booleans are compared by value; and all reference types (tables, functions, threads, userdata) are compared by identity (same object in memory).

This is useful when you need to compare two tables or userdata objects that have an __eq metamethod and you want to test whether they are literally the same object rather than semantically equal.

local a = setmetatable({}, {__eq = function() return true end})
local b = setmetatable({}, {__eq = function() return true end})
print(a == b) --> true (metamethod fires)
print(rawequal(a, b)) --> false (different objects)
print(rawequal(a, a)) --> true (same object)

Gets the real value of table[index] without invoking the __index metamethod. The first argument must be a table; the second can be any non-nil value. If the key does not exist in the table itself, rawget() returns nil rather than walking up the metatable chain.

This is useful for inspecting a table's own stored fields when a metatable-based lookup chain would otherwise intercept the access.

local fallback = {x = 10}
local t = setmetatable({}, {__index = fallback})
print(t.x) --> 10 (found via __index)
print(rawget(t, "x")) --> nil (not in t itself)
t.y = 20
print(rawget(t, "y")) --> 20 (stored directly in t)

Returns the length of a table or string without invoking the __len metamethod. The argument must be a table or string; passing any other type raises an argument error. For tables, the result is equivalent to what the # operator would return before any metamethod fires; the length of the array portion as determined by the boundary search. For strings, it returns the byte count.

local t = setmetatable({1, 2, 3}, {__len = function() return 999 end})
print(#t) --> 999 (metamethod fires)
print(rawlen(t)) --> 3 (actual array length)
print(rawlen("hello")) --> 5

Sets table[index] to value without invoking the __newindex metamethod. The first argument must be a table, the second is the key (must not be nil), and the third is the value to assign. Returns the table itself, which allows chained calls when building tables that have a __newindex guard.

This is the complement of LuaGlobals.rawget() for write operations; use it when you need to bypass a proxy table's write interception.

local log = {}
local proxy = setmetatable({}, {
    __newindex = function(_, k, v)
        table.insert(log, k)
        rawset(proxy, k, v) -- actually store the value
    end
})
rawset(proxy, "x", 42) -- bypasses __newindex; no log entry
proxy.y = 7 -- triggers __newindex; log entry created
print(proxy.x, proxy.y) --> 42  7
print(#log) --> 1 (only "y" was logged)

Runs the supplied ModuleScript and returns what the ModuleScript returned (usually a table or a function). If the ModuleScript has not been run yet, it will be executed.

If a string path is provided instead, it is first resolved to a ModuleScript relative to the script that called LuaGlobals.require(), mimicking the Unix-like semantics of Luau's require() expression.

Specifically, require-by-string's resolution semantics are as follows:

• Paths with the ./ prefix begin resolution at script.Parent.
• Paths with the ../ prefix begin resolution at script.Parent.Parent.
• Paths with the @self/ prefix begin resolution at script.
• Paths with the @game/ prefix begin resolution at game.
• Each non-prefix component in a given path corresponds to a child instance of the previous component. The exception to this is the .. component, which corresponds to the parent of the previous component.
• If the desired ModuleScript is not present at the time that LuaGlobals.require() is called, the call will fail and throw an error. In other words, require-by-string is non-blocking: it does not implicitly wait for a ModuleScript to be created.

To illustrate this, each pair of LuaGlobals.require() expressions in the example below contains two functionally equivalent calls. Redundant parentheses have been added to clarify exactly how each path component maps onto an instance.

Once the return object is created by an initial LuaGlobals.require() call of a ModuleScript, future LuaGlobals.require() calls for the same ModuleScript (on the same side of the client-server boundary) will not run the code again. Instead, a reference to the same return object created by the initial LuaGlobals.require() call will be supplied. This behavior allows for the sharing of values across different scripts, as multiple LuaGlobals.require() calls from different scripts will reference the same returned object. If the returned object is a table, any values stored within the table are shared and accessible by any script requiring that ModuleScript.

As noted above, the "object sharing" behavior does not cross the client-server boundary. This means that if a ModuleScript is accessible to both the client and server (such as by being placed in ReplicatedStorage) and LuaGlobals.require() is called from both a LocalScript as well as a Script, the code in the ModuleScript will be run twice, and the LocalScript will receive a distinct return object from the one received by the Script.

Also note that if the ModuleScript the user wants to run has been uploaded to Roblox (with the instance's name being MainModule), it can be loaded by using the LuaGlobals.require() function on the asset ID of the ModuleScript, though only on the server.

Returns all arguments after argument number index. If negative, it will return from the end of the argument list.

If the index argument is set to "#", the number of arguments that were passed after it is returned.

Sets the environment to be used by the given function. f can be a function or a number that specifies the function at that stack level: Level 1 is the function calling setfenv(). setfenv() returns the given function.

If f is 0, then setfenv() changes the environment of the running thread and returns no values.

WARNING: This function allows uncontrolled change of the global/function environment and disables script optimizations. Changes to the environment are not tracked by the script analysis tooling and may result in missing or incorrect warnings.

Sets the metatable for the given table t to newMeta. If newMeta is nil, the metatable of t is removed. Finally, this function returns the table t which was passed to it. If t already has a metatable whose __metatable metamethod is set, calling this on t raises an error.

Attempts to convert the arg into a number with a specified base to interpret the value in. If it cannot be converted, this function returns nil.

The base may be any integer between 2 and 36, inclusive. In bases above 10, the letter 'A' (in either upper or lower case) represents 10, 'B' represents 11, and so forth, with 'Z' representing 35. In base 10 (the default), the number may have a decimal part, as well as an optional exponent part. In other bases, only unsigned integers are accepted.

If a string begins with 0x and a base is not provided, the 0x is trimmed and the base is assumed to be 16, or hexadecimal.

Receives an argument of any type and converts it to a string in a reasonable format. For complete control of how numbers are converted, use string.format. If the metatable of e has a __tostring metamethod, then it will be called with e as the only argument and will return the result.

Returns the type of its only argument, coded as a string. The possible results of this function are "nil" (a string, not the value nil), "number", "string", "boolean", "table", "vector", "function", "thread", "userdata", and "buffer". The buffer and vector primitives are additions from Luau, not from Lua.

Returns the elements from the given list as separate return values, equivalent to list[i], list[i+1], ..., list[j]. By default, i is 1 and j is the length of list (as defined by the # operator). If the range is empty (i > j), no values are returned. An error is raised if the requested range is too large to fit on the stack.

local t = {10, 20, 30, 40, 50}
print(unpack(t)) --> 10  20  30  40  50
print(unpack(t, 2, 4)) --> 20  30  40

-- Common pattern: forwarding a stored argument list
local args = {1, "hello", true}
someFunction(unpack(args))

This function is similar to LuaGlobals.pcall(), except that you can set a new error handler.

xpcall() calls function f in protected mode, using err as the error handler, and passes a list of arguments. Any error inside f is not propagated; instead, xpcall() catches the error, calls the err function with the original error object, and returns a status code. Its first result is the status code (a boolean), which is true if the call succeeds without errors. In this case, xpcall() also returns all results from the call, after this first result. In case of any error, xpcall() returns false plus the result from err.

Unlike LuaGlobals.pcall(), the err function preserves the stack trace of function f, which can be inspected using debug.info() or debug.traceback().