# Express Partial Response Middleware [![NPM version](https://badge.fury.io/js/express-partial-response.png)](http://badge.fury.io/js/express-partial-response)

This Express Middleware will allow you to send a subset of a JSON object
instead of the entire object from your HTTP services. To do so, your services
will begin accepting the `?fields=` query-string that, using a simple language,
will specify which fields and sub-fields to keep and which to ignore.

If you've used the Google APIs, provided a `?fields=` query-string to get a
[Partial Response](https://developers.google.com/+/api/#partial-responses),
and wanted to do the same for your own server, now you can do so with this
middleware.

_Underneath, this middleware uses [json-mask](https://github.com/nemtsov/json-mask).
Use it directly without this middleware if you need more flexibility._

# Installation

```
npm install express-partial-response
```

# Usage

```js
const express = require('express');
const partialResponse = require('express-partial-response');
const app = express();

app.use(partialResponse());

app.get('/', (req, res) => {
  res.json({
    firstName: 'Mohandas',
    lastName: 'Gandhi',
    aliases: [
      {
        firstName: 'Mahatma',
        lastName: 'Gandhi'
      },
      {
        firstName: 'Bapu'
      }
    ]
  });
});

app.listen(4000);
```

Let's test it:

```
$ curl 'http://localhost:4000'
{"firstName":"Mohandas","lastName":"Gandhi","aliases":[{"firstName":"Mahatma","lastName":"Gandhi"},{"firstName":"Bapu"}]}

$ # Let's just get the first name
$ curl 'http://localhost:4000?fields=lastName'
{"lastName":"Gandhi"}

$ # Now, let's just get the first names directly as well as from aliases
$ curl 'http://localhost:4000?fields=firstName,aliases(firstName)'
{"firstName":"Mohandas","aliases":[{"firstName":"Mahatma"},{"firstName":"Bapu"}]}
```

**Note:** take a look at `/example`.

# Syntax

Look at [json-mask](https://github.com/nemtsov/json-mask) for the available syntax of the `fields` param.

# Options

`query` specifies the query-string to use. Defaults to `fields`

```js
app.use(
  partialResponse({
    query: 'filter'
  })
);
```

# License

MIT. See LICENSE