> For AI agents: the complete documentation index is available at https://rslint.rs/llms.txt, the full documentation bundle is available at https://rslint.rs/llms-full.txt.

# no-useless-assignment

[Added in v0.7.3](https://github.com/web-infra-dev/rslint/releases/tag/v0.7.3)
## Configuration

| Preset                   | Configured Value |
| ------------------------ | ---------------- |
| ✅ js.configs.recommended | `"error"`        |


```ts title=rslint.config.ts
import { defineConfig, js } from '@rslint/core';

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'no-useless-assignment': 'error',
    },
  },
]);
```

## Rule Details

Disallows assignments whose value is never read. A variable that is written and
then overwritten — or written on a path that ends without reading it again —
carries a value nothing observes, which usually means a mistake: a typo in the
variable name, a missing `return`, or leftover code from a refactor.

The rule only looks at variables it can follow end to end. It stays silent when
the variable is never read at all (that is `no-unused-vars`' job), when it is
read from another function, when it leaves the file — through an `export`, or
through an `/* exported name */` comment naming a global — and when the
assignment sits inside a `try` block, where the block may be abandoned before
the value is used.

Examples of **incorrect** code for this rule:

```javascript
function fn() {
	let v = 'used';
	console.log(v);
	v = 'unused';
}

function fn() {
	let v = 'unused';
	if (condition) {
		v = 'used';
		console.log(v);
		return;
	}
}

function fn() {
	let v = 'used';
	console.log(v);
	v = 'unused';
	v = 'used';
	console.log(v);
}
```

Examples of **correct** code for this rule:

```javascript
function fn() {
	let v = 'used';
	console.log(v);
	v = 'used-2';
	console.log(v);
}

function fn() {
	let v = 'used';
	if (condition) {
		v = 'used-2';
		console.log(v);
		return;
	}
	console.log(v);
}

function fn() {
	let v = 'used';
	console.log(v);
	setTimeout(() => console.log(v), 1);
	v = 'used in another scope';
}
```

## Differences from ESLint

- Destructuring follows the run-time evaluation order: the initializer or
  right-hand side produces its value first, then each element evaluates its
  computed key and default. So `let { a = x } = (x = 1, obj)` is clean here —
  the default may read `x = 1` — while ESLint reports it based on source
  positions; and in `({ [a = 1]: x } = (a = 2, obj)); console.log(a)` this
  rule reports the genuinely dead `a = 2` where ESLint reports the `a = 1`
  the log actually observes.
- Every label wrapped around a loop resolves its `break`/`continue`:
  `outer: inner: while (cond) { … continue outer; }` keeps its back edge, so
  values the next iteration reads are counted as used. ESLint attaches only
  the innermost label and falsely reports such assignments.
- A variable read from inside a parameter decorator's arguments is treated as
  used, so assignments to it are never reported:
  `const pipe = {}; class C { handler(@Body(pipe) body) {} }`. ESLint reports
  `const pipe = {}` here — a known false positive
  ([eslint/eslint#20947](https://github.com/eslint/eslint/issues/20947)).
- For deeply nested `try`/`catch`/`switch` combinations, this rule's control
  flow modeling can occasionally diverge from ESLint's own, which has open,
  accepted-but-unfixed bugs in the same area
  ([eslint/eslint#17579](https://github.com/eslint/eslint/issues/17579)) and
  its own false negatives on some such shapes. Matching it exactly there is
  hard to pin down, so it is left as a known gap. These shapes are rare in
  practice; in the large majority of real code this rule reports the same
  findings as ESLint.

## Original Documentation

- [ESLint: no-useless-assignment](https://eslint.org/docs/latest/rules/no-useless-assignment)
- [Source code](https://github.com/eslint/eslint/blob/v10.8.1/lib/rules/no-useless-assignment.js)