> 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.

# restrict-template-expressions

[Added in v0.1.4](https://github.com/web-infra-dev/rslint/releases/tag/v0.1.4)
## Configuration

| Preset                              | Configured Value                                                                                                                    |
| ----------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- |
| ✅ ts.configs.recommendedTypeChecked | `"error"`                                                                                                                           |
| ✅ ts.configs.strictTypeChecked      | `["error",{"allowAny":false,"allowBoolean":false,"allowNever":false,"allowNullish":false,"allowNumber":false,"allowRegExp":false}]` |


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

export default defineConfig([
  ts.configs.recommended,
  {
    rules: {
      '@typescript-eslint/restrict-template-expressions': 'error',
    },
  },
]);
```

## Rule Details

Enforce template literal expressions to be of `string` type. When a value is interpolated into a template literal (`${expr}`), it is implicitly converted to a string, which produces results such as `"[object Object]"` for plain objects. This rule restricts which types may be interpolated.

By default, primitives that stringify predictably are permitted (`number`, `bigint`, `boolean`, `null`, `undefined`, `any`, `RegExp`), along with `Error`, `URL`, and `URLSearchParams` and their subclasses.

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

```typescript
declare const obj: object;
const msg = `result: ${obj}`;

declare const arr: string[];
const msg2 = `items: ${arr}`;

declare const sym: symbol;
const msg3 = `symbol: ${sym}`;
```

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

```typescript
const name = 'world';
const greeting = `Hello, ${name}`;

declare const obj: object;
const msg = `result: ${JSON.stringify(obj)}`;

declare const arr: string[];
const msg2 = `items: ${arr.join(', ')}`;
```

## Options

| Option         | Type                                 | Default                                                        | Description                                                                    |
| -------------- | ------------------------------------ | -------------------------------------------------------------- | ------------------------------------------------------------------------------ |
| `allow`        | `(string \| TypeOrValueSpecifier)[]` | `[{ from: 'lib', name: ['Error', 'URL', 'URLSearchParams'] }]` | Additional types to permit, matched against the type or any of its base types. |
| `allowAny`     | `boolean`                            | `true`                                                         | Permit `any` typed values.                                                     |
| `allowArray`   | `boolean`                            | `false`                                                        | Permit arrays and tuples whose element type is itself permitted.               |
| `allowBoolean` | `boolean`                            | `true`                                                         | Permit `boolean` typed values.                                                 |
| `allowNever`   | `boolean`                            | `false`                                                        | Permit `never` typed values.                                                   |
| `allowNullish` | `boolean`                            | `true`                                                         | Permit `null` and `undefined`.                                                 |
| `allowNumber`  | `boolean`                            | `true`                                                         | Permit `number` and `bigint` typed values.                                     |
| `allowRegExp`  | `boolean`                            | `true`                                                         | Permit `RegExp` typed values.                                                  |

To require every interpolated value to be a `string`, empty the `allow` list and turn each `allow*` option off:

```json
{
  "@typescript-eslint/restrict-template-expressions": [
    "error",
    {
      "allow": [],
      "allowAny": false,
      "allowBoolean": false,
      "allowNever": false,
      "allowNullish": false,
      "allowNumber": false,
      "allowRegExp": false
    }
  ]
}
```

## Original Documentation

- [typescript-eslint: restrict-template-expressions](https://typescript-eslint.io/rules/restrict-template-expressions)
- [Source code](https://github.com/typescript-eslint/typescript-eslint/blob/v8.67.0/packages/eslint-plugin/src/rules/restrict-template-expressions.ts)