# expired
> Calculate when HTTP responses expire from the cache headers
[](https://travis-ci.org/lukechilds/expired) [](https://coveralls.io/github/lukechilds/expired?branch=master)
`expired` accepts HTTP headers as an argument and will return information on when the resource will expire. `Cache-Control` and `Expires` headers are supported, if both exist `Cache-Control` takes priority.
## Install
```shell
npm install --save expired
```
## Usage
```js
const expired = require('expired');
const headers = `
Age: 0
Cache-Control: public, max-age=300
Content-Encoding: gzip
Content-Type: application/json;charset=utf-8
Date: Fri, 23 Dec 2016 05:50:31 GMT
Last-Modified: Fri, 23 Dec 2016 05:23:23 GMT`;
expired(headers);
// false
expired.in(headers);
// 500000
expired.on(headers);
// Date('2016-12-23T05:55:31.000Z')
delay(600000).then(() => {
expired(headers);
// true
expired.in(headers);
// -100000
expired.on(headers);
// Date('2016-12-23T05:55:31.000Z')
});
```
Many HTTP modules will parse response headers into an object for you. `expired` will also accept headers in this format:
```js
const expired = require('expired');
const headers = {
'age': '0',
'cache-control': 'public, max-age=300',
'content-encoding': 'gzip',
'content-type': 'application/json;charset=utf-8',
'date': 'Fri, 23 Dec 2016 05:50:31 GMT',
'last-modified': 'Fri, 23 Dec 2016 05:23:23 GMT'
};
expired(headers);
// false
```
## Pure Usage
You can make the functions pure by passing in a JavaScript `Date` object to compare to instead of depending on `new Date()` . This isn't necessary for `expired.on` as it doesn't compare dates and is already pure.
The following are all pure functions:
```js
const headers = `...` ;
const date = new Date();
expired(headers, date);
expired.in(headers, date);
expired.on(headers);
```
## API
### expired(headers, [date])
Returns a boolean relating to whether the resource has expired or not. `true` means it's expired, `false` means it's fresh.
### expired.in(headers, [date])
Returns the amount of milliseconds from the current date until the resource will expire. If the resource has already expired it will return a negative integer.
### expired.on(headers)
Returns a JavaScript `Date` object for the date the resource will expire.
## License
MIT © Luke Childs
