koa-json-mask

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

If you've used the Google APIs, provided a ?fields= query-string to get a Partial Response, and wanted to do the same for your own server, you can do so with this middleware.

The difference between koa-json-filter and koa-json-mask is that this middleware supports filtering parts deep within objects. If you only need to be able to filter top-level params of objects in the response use filter, and if you need more power user mask.

Underneath, this middleware uses json-mask. Use it directly without this middleware if you need more flexibility.

Installation

$ npm install koa-json-mask

In order to use this plugin with the previous version of Koa using generator functions, please use version 0.3.2

$ npm install koa-json-mask@0.3.2

Options

• name querystring param name defaulting to "fields"

Example

Object responses

Script:

const Koa = require('koa');
const mask = require('koa-json-mask');

const app = new Koa();

app.use(mask());

app.use(async ctx => {
  ctx.body = {
    name: 'tobi',
    packages: 5,
    friends: ['abby', 'loki', 'jane'],
    location: {
      id: '342',
      name: 'London'
    }
  };
});

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

Response:

$ GET /?fields=name,location/name
{
  "name": "tobi",
  "location": {
    "name": "London"
  }
}

Array responses

Script:

const Koa = require('koa');
const mask = require('koa-json-mask');

const app = new Koa();

app.use(mask());

app.use(async ctx => {
  ctx.body = [
    {
      name: 'tobi',
      packages: 5,
      friends: ['abby', 'loki', 'jane'],
      location: {
        id: '342',
        name: 'London'
      }
    },
    {
      name: 'loki',
      packages: 2,
      friends: ['loki', 'jane'],
      location: {
        id: '62',
        name: 'New York'
      }
    }
  ];
});

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

Response:

$ GET /?fields=name,location/name
[
  {
    "name": "tobi",
    "location": {
      "name": "London"
    }
  },
  {
    "name": "loki",
    "location": {
      "name": "New York"
    }
  }
]

Syntax

The syntax is loosely based on XPath:

• a,b,c comma-separated list will select multiple fields
• a/b/c path will select a field from its parent
• a(b,c) sub-selection will select many fields from a parent
• a/*/c the star * wildcard will select all items in a field

More examples

For more examples, take a look at the examples section of the json-mask README.

License

MIT