---
title: Arguments
type: reference
summary: Pass arguments to SWR fetcher functions.
prerequisites:
  - /docs/getting-started
related:
  - /docs/data-fetching
  - /docs/conditional-fetching
---

# Arguments



By default, `key` will be passed to `fetcher` as the argument. So the following 3 expressions are equivalent:

```js
useSWR('/api/user', () => fetcher('/api/user'))
useSWR('/api/user', url => fetcher(url))
useSWR('/api/user', fetcher)
```

## Multiple Arguments

In some scenarios, it's useful to pass multiple arguments (can be any value or object) to the `fetcher` function.
For example an authorized fetch request:

```js
useSWR('/api/user', url => fetchWithToken(url, token))
```

This is **incorrect**. Because the identifier (also the cache key) of the data is `'/api/user'`,
even if `token` changes, SWR will still use the same key and return the wrong data.

Instead, you can use an **array** as the `key` parameter, which contains multiple arguments of `fetcher`:

```js
const { data: user } = useSWR(['/api/user', token], ([url, token]) => fetchWithToken(url, token))
```

The `fetcher` function accepts the `key` parameter as is, and the cache key will also be associated with the entire `key` argument. In the above example, `url` and `token` are both tied to the cache key.

<Callout emoji="⚠️">
  In the previous versions (\< 2.0.0), The `fetcher` function will receive the spreaded arguments from original `key` when the `key` argument is array type. E.g., key `[url, token]` will become 2 arguments `(url, token)` for `fetcher` function.
</Callout>

## Passing Objects

<Callout>
  Since SWR 1.1.0, object-like keys will be serialized under the hood automatically.
</Callout>

Say you have another function that fetches data with a user scope: `fetchWithUser(api, user)`. You can do the following:

```js
const { data: user } = useSWR(['/api/user', token], fetchWithToken)

// ...and then pass it as an argument to another useSWR hook
const { data: orders } = useSWR(user ? ['/api/orders', user] : null, fetchWithUser)
```

You can directly pass an object as the key, and `fetcher` will receive that object too:

```js
const { data: orders } = useSWR({ url: '/api/orders', args: user }, fetcher)
```

<Callout emoji="⚠️">
  In older versions (\< 1.1.0), SWR **shallowly** compares the arguments on every render, and triggers revalidation if any of them has changed.
</Callout>