---
url: /docs/guide/usage/linter/rules/typescript/no-base-to-string.md
---

### What it does

This rule requires `toString()` and `toLocaleString()` calls to only be called on objects which provide useful information when stringified.

### Why is this bad?

JavaScript's `toString()` method returns '\[object Object]' on plain objects, which is not useful information. This rule prevents `toString()` and `toLocaleString()` from being called on objects that return less useful strings.

### Examples

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

```ts
// These will evaluate to '[object Object]'
({}).toString();
({ foo: "bar" }).toString();
({ foo: "bar" }).toLocaleString();

// This will evaluate to 'Symbol()'
Symbol("foo").toString();
```

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

```ts
const someString = "Hello world";
someString.toString();

const someNumber = 42;
someNumber.toString();

const someBoolean = true;
someBoolean.toString();

class CustomToString {
  toString() {
    return "CustomToString";
  }
}
new CustomToString().toString();
```

## Configuration

This rule accepts a configuration object with the following properties:

### checkUnknown

type: `boolean`

default: `false`

Whether to also check values of type `unknown`.
When `true`, calling toString on `unknown` values will be flagged.
Default is `false`.

### ignoredTypeNames

type: `string[]`

default: `["Error", "RegExp", "URL", "URLSearchParams"]`

A list of type names to ignore when checking for unsafe toString usage.
These types are considered safe to call toString on even if they don't
provide a custom implementation.

## How to use

## Version

This rule was added in v1.12.0.

## References