# Optional ESLint config

Source: https://smartassertions.dev/eslint-config-rules/
Index of every page: https://smartassertions.dev/llms.txt

The `@kensio/smartass` package also exports an optional ESLint flat config that discourages less
specific assertion usage. For example:

```typescript
assertIdentical(foo.length, 2);
// suggested improvement:
assertArrayLength(foo, 2);
```

You can use this in your ESLint config like this:

```typescript
import { defineConfig } from "eslint/config";
import tseslint from "typescript-eslint";

import { smartassPreferSpecificAssertions } from "@kensio/smartass/eslint";

export default defineConfig(
  ...tseslint.configs.recommended,
  ...smartassPreferSpecificAssertions,
);
```

The same suggestions are available as an [Oxlint plugin](https://smartassertions.dev/oxlint-plugin-rules/). Both are generated
from a single table of selectors, so the two linters report identically and you only need whichever
one you already run.

Some more examples of the replacements that the ESLint rules will suggest:

- `assertIdentical(value, true)` → `assertTrue(value)`
- `assertIdentical(value, false)` → `assertFalse(value)`
- `assertIdentical(value, undefined)` → `assertUndefined(value)`
- `assertTrue(value != null)` → `assertNonNullable(value)`
- `assertIdentical(typeof value, "string")` → `assertTypeString(value)`
- `assertIdentical(value instanceof MyClass, true)` → `assertInstanceOf(value, MyClass)`
- `assertIdentical("key" in object, true)` → `assertObjectHasProperty(object, "key")`
- `assertIdentical(value.length, expected)` → `assertArrayLength()` etc.
- `assertIdentical(value.size, expected)` → `assertSetSize()` etc.
- `assertTrue(array.length > 0)` → `assertArrayNotEmpty(array)`
- `assertTrue(value.includes(expected))` → `assertStringIncludes()` etc.
- `assertTrue(value.startsWith(prefix))` → `assertStringStartsWith(value, prefix)`
- `assertTrue(value.endsWith(suffix))` → `assertStringEndsWith(value, suffix)`
- `assertTrue(stats.isDirectory())` → `assertDirectoryExists()` etc.