> ## Documentation Index
> Fetch the complete documentation index at: https://docs.projectreal.gg/llms.txt
> Use this file to discover all available pages before exploring further.

# setupvalue

> Replaces one upvalue in a Lua function or stack level by one-based index. Invalid stack levels raise "Level out of range", non-Lua functions raise "Lua function expected", indexes below 1 raise "Upvalue index starts at 1", and indexes past the available upvalues raise "Upvalue index is out of range". debug.setupvalue is an alias.

Replaces one upvalue in a Lua function or stack level by one-based index. Invalid stack levels raise "Level out of range", non-Lua functions raise "Lua function expected", indexes below 1 raise "Upvalue index starts at 1", and indexes past the available upvalues raise "Upvalue index is out of range". debug.setupvalue is an alias.

## Syntax

```lua theme={null}
setupvalue(target: function | number, index: number, value: any)
```

## Aliases

* `debug.setupvalue`

## Arguments

| Name     | Type                 | Required | Description                                            |
| -------- | -------------------- | -------- | ------------------------------------------------------ |
| `target` | `function \| number` | Yes      | Lua function or stack level whose upvalue is modified. |
| `index`  | `number`             | Yes      | One-based upvalue index.                               |
| `value`  | `any`                | Yes      | New value for the upvalue.                             |

## Example

Replace one upvalue in a Lua closure or stack level.

```lua theme={null}
local captured = "before"

local function target()
    return captured
end

print(target())

setupvalue(target, 1, "after")
print(target())

debug.setupvalue(target, 1, "done")
print(target())
```