---
title: MARKLESS_STATE_OPTIONAL_CHAIN_WRITE
description: "Code writes to state through optional chaining, like a?.b = 1."
sidebar: { hidden: true }
search: { keywords: ["STATE_OPTIONAL_CHAIN_WRITE","state optional chain write","markless error"] }
pagination: false
---

**Error** from the compiler, while it builds your `.tsrx` files.

## What happened

Optional chaining can skip a write when part of the path is missing. Markless needs every write to have a definite target.

Markless prints the message, the reason, and a suggestion:

```text
MARKLESS_STATE_OPTIONAL_CHAIN_WRITE: Cannot write to "<target>" through optional chaining because graph writes must have definite targets.
Optional chaining can skip the method call and its arguments at runtime. The current graph write artifact cannot preserve that short-circuit behavior safely across resume.
Guard explicitly before mutating graph state, or initialize the state path so the collection method call always has a definite target.
https://markless.dev/errors/MARKLESS_STATE_OPTIONAL_CHAIN_WRITE
```

Words in angle brackets change from case to case.

## How to fix it

Check the value with an `if` before you write. Or give the state a start value so the path always exists.

## Where it comes from

`@markless/compiler` raises this code. Source:

- [packages/compiler/src/passes/state-lowering.ts](https://github.com/compiled-run/markless/blob/main/packages/compiler/src/passes/state-lowering.ts)

Read [how to read a Markless error](/tooling/diagnostics), or go back to [all error codes](/errors).