## Features
- [classic debounced callback](#debounced-callbacks)
- [**value** debouncing](#simple-values-debouncing)
- [cancel, maxWait and memoization](#advanced-usage)
## Install
```sh
yarn add use-debounce
# or
npm i use-debounce --save
```
## Copy paste guidance:
### use-debounce
Simple usage: https://codesandbox.io/s/kx75xzyrq7
Debounce HTTP request: https://codesandbox.io/s/rr40wnropq
Debounce HTTP request with `leading` param: https://codesandbox.io/s/cache-example-with-areas-and-leading-param-119r3i
### use-debounce callback
Simple usage: https://codesandbox.io/s/x0jvqrwyq
Combining with native event listeners: https://codesandbox.io/s/32yqlyo815
Cancelling, maxWait and memoization: https://codesandbox.io/s/4wvmp1xlw4
HTTP requests: https://codesandbox.io/s/use-debounce-callback-http-y1h3m6
## Changelog
https://github.com/xnimorz/use-debounce/blob/master/CHANGELOG.md
## Simple values debouncing
According to https://twitter.com/dan_abramov/status/1060729512227467264
```javascript
import React, { useState } from 'react';
import { useDebounce } from 'use-debounce';
export default function Input() {
const [text, setText] = useState('Hello');
const [value] = useDebounce(text, 1000);
return (
{
setText(e.target.value);
}}
/>
Actual value: {text}
Debounce value: {value}
);
}
```
This hook compares prev and next value using shallow equal. It means, setting an object `{}` will trigger debounce timer. If you have to compare objects (https://github.com/xnimorz/use-debounce/issues/27#issuecomment-496828063), you can use `useDebouncedCallback`, that is explained below:
## Debounced callbacks
Besides `useDebounce` for values you can debounce callbacks, that is the more commonly understood kind of debouncing.
Example with Input (and react callbacks): https://codesandbox.io/s/x0jvqrwyq
```js
import { useDebouncedCallback } from 'use-debounce';
function Input({ defaultValue }) {
const [value, setValue] = useState(defaultValue);
// Debounce callback
const debounced = useDebouncedCallback(
// function
(value) => {
setValue(value);
},
// delay in ms
1000
);
// you should use `e => debounced(e.target.value)` as react works with synthetic events
return (
debounced(e.target.value)} />
Debounced value: {value}
);
}
```
Example with Scroll (and native event listeners): https://codesandbox.io/s/32yqlyo815
```js
function ScrolledComponent() {
// just a counter to show, that there are no any unnessesary updates
const updatedCount = useRef(0);
updatedCount.current++;
const [position, setPosition] = useState(window.pageYOffset);
// Debounce callback
const debounced = useDebouncedCallback(
// function
() => {
setPosition(window.pageYOffset);
},
// delay in ms
800
);
useEffect(() => {
const unsubscribe = subscribe(window, 'scroll', debounced);
return () => {
unsubscribe();
};
}, []);
return (
Debounced top position: {position}
Component rerendered {updatedCount.current} times
);
}
```
### Returned value from `debounced()`
Subsequent calls to the debounced function `debounced` return the result of the last func invocation.
Note, that if there are no previous invocations it's mean you will get undefined. You should check it in your code properly.
Example:
```javascript
it('Subsequent calls to the debounced function `debounced` return the result of the last func invocation.', () => {
const callback = jest.fn(() => 42);
let callbackCache;
function Component() {
const debounced = useDebouncedCallback(callback, 1000);
callbackCache = debounced;
return null;
}
Enzyme.mount();
const result = callbackCache();
expect(callback.mock.calls.length).toBe(0);
expect(result).toBeUndefined();
act(() => {
jest.runAllTimers();
});
expect(callback.mock.calls.length).toBe(1);
const subsequentResult = callbackCache();
expect(callback.mock.calls.length).toBe(1);
expect(subsequentResult).toBe(42);
});
```
### Advanced usage
#### Cancel, maxWait and memoization
1. Both `useDebounce` and `useDebouncedCallback` works with `maxWait` option. This params describes the maximum time func is allowed to be delayed before it's invoked.
2. You can cancel debounce cycle, by calling `cancel` callback
The full example you can see here https://codesandbox.io/s/4wvmp1xlw4
```javascript
import React, { useState } from 'react';
import ReactDOM from 'react-dom';
import { useDebouncedCallback } from 'use-debounce';
function Input({ defaultValue }) {
const [value, setValue] = useState(defaultValue);
const debounced = useDebouncedCallback(
(value) => {
setValue(value);
},
500,
// The maximum time func is allowed to be delayed before it's invoked:
{ maxWait: 2000 }
);
// you should use `e => debounced(e.target.value)` as react works with synthetic events
return (
debounced(e.target.value)} />
Debounced value: {value}
);
}
const rootElement = document.getElementById('root');
ReactDOM.render(, rootElement);
```
#### Flush method
`useDebouncedCallback` has `flush` method. It allows to call the callback manually if it hasn't fired yet. This method is handy to use when the user takes an action that would cause the component to unmount, but you need to execute the callback.
```javascript
import React, { useState } from 'react';
import { useDebouncedCallback } from 'use-debounce';
function InputWhichFetchesSomeData({ defaultValue, asyncFetchData }) {
const debounced = useDebouncedCallback(
(value) => {
asyncFetchData;
},
500,
{ maxWait: 2000 }
);
// When the component goes to be unmounted, we will fetch data if the input has changed.
useEffect(
() => () => {
debounced.flush();
},
[debounced]
);
return debounced(e.target.value)} />;
}
```
#### isPending method
`isPending` method shows whether component has pending callbacks. Works for both `useDebounce` and `useDebouncedCallback`:
```javascript
import React, { useCallback } from 'react';
function Component({ text }) {
const debounced = useDebouncedCallback(useCallback(() => {}, []), 500);
expect(debounced.isPending()).toBeFalsy();
debounced();
expect(debounced.isPending()).toBeTruthy();
debounced.flush();
expect(debounced.isPending()).toBeFalsy();
return {text};
}
```
#### leading/trailing calls
Both `useDebounce` and `useDebouncedCallback` work with the `leading` and `trailing` options. `leading` param will execute the function once immediately when called. Subsequent calls will be debounced until the timeout expires. `trailing` option controls whenever to call the callback after timeout again.
For more information on how leading debounce calls work see: https://lodash.com/docs/#debounce
```javascript
import React, { useState } from 'react';
import { useDebounce } from 'use-debounce';
export default function Input() {
const [text, setText] = useState('Hello');
const [value] = useDebounce(text, 1000, { leading: true });
// value is updated immediately when text changes the first time,
// but all subsequent changes are debounced.
return (
{
setText(e.target.value);
}}
/>
Actual value: {text}
Debounce value: {value}
);
}
```
#### Options:
You can provide additional options as a third argument to both `useDebounce` and `useDebouncedCallback`:
| option | default | Description | Example |
| ---------- | ----------------------------- | -------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------- |
| maxWait | - | Describes the maximum time func is allowed to be delayed before it's invoked | https://github.com/xnimorz/use-debounce#cancel-maxwait-and-memoization |
| leading | - | This param will execute the function once immediately when called. Subsequent calls will be debounced until the timeout expires. | https://github.com/xnimorz/use-debounce#leading-calls |
| trailing | true | This param executes the function after timeout. | https://github.com/xnimorz/use-debounce#leading-calls |
| equalityFn | (prev, next) => prev === next | [useDebounce ONLY] Comparator function which shows if timeout should be started | |
## useThrottledCallback
You are able to use throttled callback with this library also (starting 5.2.0 version).
For this purpose use:
```
import useThrottledCallback from 'use-debounce/useThrottledCallback';
```
or
```
import { useThrottledCallback } from 'use-debounce';
```
Several examples:
1. Avoid excessively updating the position while scrolling.
```js
const scrollHandler = useThrottledCallback(updatePosition, 100);
window.addEventListener('scroll', scrollHandler);
```
2. Invoke `renewToken` when the click event is fired, but not more than once every 5 minutes.
```js
const throttled = useThrottledCallback(renewToken, 300000, { 'trailing': false })
```
All the params for `useThrottledCallback` are the same as for `useDebouncedCallback` except `maxWait` option. As it's not needed for throttle callbacks.
# Special thanks:
[@tryggvigy](https://github.com/tryggvigy) — for managing lots of new features of the library like trailing and leading params, throttle callback, etc;
[@omgovich](https://github.com/omgovich) — for reducing bundle size.
