---
id: effect
title: Effect
---
_Effect_ is a container for async function.
It can be safely used in place of the original async function.
The only requirement for function:
- **Should** have zero or one argument
#### Arguments
1. `params` (_Params_): parameters
#### Returns
(_`Future`_)
### Effect Methods
- [`use(fn)`](#use)
- [`watch(watcher)`](#watch)
- [`prepend(fn)`](#prepend)
### Effect Properties
- [`done`](#done)
- [`fail`](#fail)
## Effect Methods
### <a id='use'></a>[`use(fn)`](#use)
#### Returns
(_`Effect`_): A container for async function.
<hr>
### <a id='watch'></a>[`watch(watcher)`](#watch)
#### Returns
(_`Subscription`_): Unsubscribe function
<hr>
### <a id='prepend'></a>[`prepend(fn)`](#prepend)
#### Returns
(_`Event`_): An intention to change state.
<hr>
## Effect Properties