Middleware allowing the client to filter the response to only what they need, reducing the amount of traffic over the wire using the ?filter=foo,bar,baz querystring parameter.

JSONSelect would also be great for this but I find it's a little too complicated for the average use-case, so this is just a simple key filter.

Installation

$ npm install @koa/json-filter

Please note that if you're using an earlier version of koa 2 with function generator you need to install the older version 0.0.1

$ npm install koa-json-filter@0.0.1

Options

• name querystring param defaulting to "filter"

Filtering customization

You may also set ctx.filter to an array of names to filter on, for example by using a header field X-Filter: name,email.

Example

Object responses

Script:

const Koa = require('koa');
const filter = require('@koa/json-filter');

const app = new Koa();

app.use(filter());

app.use(async ctx => {
  ctx.body = {
    name: 'tobi',
    email: 'tobi@segment.io',
    packages: 5,
    friends: ['abby', 'loki', 'jane']
  };
});

app.listen(3000);
console.log('app listening on port 3000');

Response:

$ GET /?filter=name
{
  "name": "tobi"
}

Array responses

Script:

const Koa = require('koa');
const filter = require('@koa/json-filter');

const app = new Koa();

app.use(filter());

app.use(async ctx => {
  ctx.body = [
    {
      name: 'tobi',
      email: 'tobi@segment.io',
      packages: 5,
      friends: ['abby', 'loki', 'jane']
    },
    {
      name: 'loki',
      email: 'loki@segment.io',
      packages: 2,
      friends: ['loki', 'jane']
    },
    {
      name: 'jane',
      email: 'jane@segment.io',
      packages: 2,
      friends: []
    },
    {
      name: 'ewald',
      email: 'ewald@segment.io',
      packages: 2,
      friends: ['tobi']
    }
  ];
});

app.listen(3000);
console.log('app listening on port 3000');

Response:

$ GET /?filter=name,email
[
  {
    "name": "tobi",
    "email": "tobi@segment.io"
  },
  {
    "name": "loki",
    "email": "loki@segment.io"
  },
  {
    "name": "jane",
    "email": "jane@segment.io"
  },
  {
    "name": "ewald",
    "email": "ewald@segment.io"
  }
]

License

MIT