npm package: @kapouer/express-cache-response-directive
Description: ExpressJS middleware that gives Response objects an intuitive .cacheControl method to set Cache-Control headers.
Latest version: 2.1.0

# express-cache-response-directive

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Middleware for ExpressJS that defines a `cacheControl` method to set `Cache-Control` headers.

This middleware doesn't define legacy Expires headers. For compatibility with old HTTP/1.0 agents combine it with [express-legacy-expires](https://github.com/dantman/express-legacy-expires).

## Install

```bash
npm install express-cache-response-directive
```

## Usage

```js
const cacheResponseDirective = require('express-cache-response-directive');
```

```js
app.use(cacheResponseDirective());
```

```js
app.get('/', function(req, res, next) {
  res.cacheControl({maxAge: 300});
  // ...
});
```

### res.cacheControl([pattern], [options])

The method added by the middleware accepts an optional string pattern and an object of Cache-Control options. Both are optional but at least one of them should be specified.

See the [HTTP/1.1 Standard's Cache-Control sections](http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9) for information on the usage of Cache-Control directives.

#### Patterns

String patterns are defined for simple directives so you can simply write `res.cacheControl("public");` instead of having to always write `res.cacheControl({'public': true});`. Patterns can be combined with options `res.cacheControl("public", {mustRevalidate: true});`.

##### "public"

```js
res.cacheControl("public");
// Cache-Control: public
```

##### "private"

```js
res.cacheControl("private");
// Cache-Control: private
```

##### "no-cache"

```js
res.cacheControl("no-cache");
// Cache-Control: no-cache
```

##### "no-store"

```js
res.cacheControl("no-store");
// Cache-Control: no-cache, no-store
```

#### Options

Each Cache-Control response directive defined in HTTP/1.1 has an option that can be defined.

- Options for directives that use a delta time accept a number as a value.
- Time values may also be expressed as strings like "3 min", "1h", "5 days".
- Options that optionally accept field names accept `true` for the normal non-field directive and for the with field-name directive accept either a string or an array of strings for the field names.
- The remaining directives that don't have a value simply accept a truthy value.

The public, private, no-cache, and no-store directives are exclusive only one may be specified. With the exception that no-cache and no-store may be defined together.

##### public

```js
res.cacheControl({'public': true});
// Cache-Control: public
```

##### private

```js
res.cacheControl({'private': true});
// Cache-Control: private
```

```js
res.cacheControl({'private': "X-Private"});
// Cache-Control: private="X-Private"
```

```js
res.cacheControl({'private': ["X-Private-1", "X-Private-2"]});
// Cache-Control: private="X-Private-1, X-Private-2"
```

##### no-cache

```js
res.cacheControl({'no-cache': true});
res.cacheControl({noCache: true});
// Cache-Control: no-cache
```

```js
res.cacheControl({noCache: "X-Uncached"});
// Cache-Control: no-cache="X-Uncached"
```

```js
res.cacheControl({noCache: ["X-Uncached-1", "X-Uncached-2"]});
// Cache-Control: no-cache="X-Uncached-1, X-Uncached-2"
```

##### no-store

```js
res.cacheControl({'no-store': true});
res.cacheControl({noStore: true});
// Cache-Control: no-cache, no-store
```

- `no-store` also implies `no-cache` because some browsers have begun treating no-cache the same way they treat no-store.

##### max-age

```js
res.cacheControl({'max-age': 300});
res.cacheControl({maxAge: 300});
res.cacheControl({maxAge: "5min"});
// Cache-Control: public, max-age=300
```

- `max-age` implies public if none of private, no-cache, or no-store is defined, so you can define it alone.

##### s-maxage

```js
res.cacheControl({'s-maxage': 300});
res.cacheControl({sMaxage: 300});
res.cacheControl({sMaxAge: 300});
// Cache-Control: public, s-maxage=300
```

- `s-maxage` supports `sMaxAge` in addition to the standard camel-case conversion `sMaxage` due to the potential confusion of the `max-age` to `maxAge` conversion.

##### must-revalidate

```js
res.cacheControl({'must-revalidate': true});
res.cacheControl({mustRevalidate: true});
// Cache-Control: must-revalidate
```

##### proxy-revalidate

```js
res.cacheControl({'proxy-revalidate': true});
res.cacheControl({proxyRevalidate: true});
// Cache-Control: proxy-revalidate
```

##### no-transform

```js
res.cacheControl({noTransform: true});
res.cacheControl({'no-transform': true});
// Cache-Control: no-transform
```

## License

[MIT](LICENSE)