---
url: /docs/guide/usage/linter/rules/node/handle-callback-err.md
---

### What it does

This rule expects that when you're using the callback pattern in Node.js you'll handle the error.

### Why is this bad?

In Node.js, a common pattern for dealing with asynchronous behavior is called the callback pattern.
This pattern expects an `Error` object or `null` as the first argument of the callback.
Forgetting to handle these errors can lead to some really strange behavior in your application.

```js
function loadData(err, data) {
  doSomething(); // forgot to handle error
}
```

### Examples

Examples of **incorrect** code for this rule with the default `"err"` parameter name:

```js
function loadData(err, data) {
  doSomething();
}
```

Examples of **correct** code for this rule with the default `"err"` parameter name:

```js
function loadData(err, data) {
  if (err) {
    console.log(err.stack);
  }
  doSomething();
}

function generateError(err) {
  if (err) {
  }
}
```

Examples of correct code for this rule with a sample `"error"` parameter name:

```js
function loadData(error, data) {
  if (error) {
    console.log(error.stack);
  }
  doSomething();
}
```

## Configuration

The rule takes a single string option: the name of the error parameter.

This can be either:

* an exact name (e.g. `"err"`, `"error"`)
* a regexp pattern (e.g. `"^(err|error)$"`)

If the configured name of the error variable begins with a `^` it is considered to be a regexp pattern.
Invalid regexp patterns are rejected during configuration parsing.

Default: `"err"`.

type: `string`

## How to use

## Version

This rule was added in v1.56.0.

## References