defer

defer(fn) registers a cleanup function to run immediately after the top-level hook exits. Essential for preventing zombie processes and memory leaks.

Signature

defer(fn)

sync

Note

Hook-scoped: Cleanup runs when the main stage (e.g., before_fetch) finishes, even if defer was called inside a helper function.

Note

Synchronous only: You cannot use async functions (like http_post or cdp.launch) inside defer. Resource close methods (such as browser:close() or page:close()) are synchronous and fully safe to use. For async orchestration and post-cycle tasks, use defer.lua.

Parameters

Param	Type	Description
fn	function	Cleanup function to call after the hook exits

Returns

None.

Example

function override_fetch(request, ctx)
    local browser = cdp.launch({ headless = true })
    defer(function() browser:close() end) -- Always closes

    local page = browser:attach()
    page:open(request.url)
    return { status = 200, body = page:content() }
end

See Also

• Lifecycle - Full lifecycle documentation