---
url: /docs/guide/usage/linter/rules/promise/prefer-catch.md
---

### What it does

Prefer `catch` to `then(a, b)` and `then(null, b)`. This rule disallows the passing of an
argument into the second parameter of `then` calls for handling promise errors.

### Why is this bad?

A `then` call with two arguments can make it more difficult to recognize that a catch error
handler is present. Another issue with using the second argument in `then` calls is that
the ordering of promise error handling is less obvious.

For example on first glance it may appear that `prom.then(fn1, fn2)` is equivalent to
`prom.then(fn1).catch(fn2)`. However they aren't equivalent. In fact
`prom.catch(fn2).then(fn1)` is the equivalent. This kind of confusion is a good reason for
preferring explicit `catch` calls over passing an argument to the second parameter of
`then` calls.

### Examples

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

```js
prom.then(fn1, fn2);

prom.then(null, fn2);
```

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

```js
prom.catch(fn2).then(fn1);

prom.catch(fn2);
```

## How to use

## Version

This rule was added in v0.15.14.

## References