JSON Mask   

This is a tiny language and an engine for selecting specific parts of a JS object, hiding/masking the rest.

``js
var mask = require('json-mask');
mask({ p: { a: 1, b: 2 }, z: 1 }, 'p/a,z'); // {p: {a: 1}, z: 1}
`

The main difference between JSONPath / JSONSelect and this engine is that JSON Mask
preserves the structure of the original input object.
Instead of returning an array of selected sub-elements (e.g. [{a: 1}, {z: 1}] from example above),
it filters-out the parts of the object that you don't need,
keeping the structure unchanged: {p: {a: 1}, z: 1}.

This is important because JSON Mask was designed with HTTP resources in mind,
the structure of which I didn't want to change after the unwanted fields
were masked / filtered.

If you've used the Google APIs, and provided a ?fields= query-string to get a
Partial Response, you've
already used this language. The desire to have partial responses in
my own Node.js-based HTTP services was the reason I wrote JSON Mask.

_For express users, there's an
express-partial-response middleware.
It will integrate with your existing services with no additional code
if you're using res.json() or res.jsonp(). And if you're already using koa
check out the koa-json-mask middleware._

This library has no dependencies. It works in Node as well as in the browser.

Note: the 1.5KB (gz), or 4KB (uncompressed) browser build is in the /build folder.

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

Take a look at test/index-test.js for examples of all of these and more.

Grammar

`
Props ::= Prop | Prop "," Props
Prop ::= Object | Array
Object ::= NAME | NAME "/" Prop
Array ::= NAME "(" Props ")"
NAME ::= ? all visible characters except "\" ? | EscapeSeq | Wildcard
Wildcard ::= "*"
EscapeSeq ::= "\" ? all visible characters ?
`

Examples

Identify the fields you want to keep:

`js
var fields = 'url,object(content,attachments/url)';
`

From this sample object:

`js
var originalObj = {
id: 'z12gtjhq3qn2xxl2o224exwiqruvtda0i',
url: 'https://plus.google.com/102817283354809142195/posts/F97fqZwJESL',
object: {
objectType: 'note',
content:
'A picture... of a space ship... launched from earth 40 years ago.',
attachments: [
{
objectType: 'image',
url: 'http://apod.nasa.gov/apod/ap110908.html',
image: { height: 284, width: 506 }
}
]
},
provider: { title: 'Google+' }
};
`

Here's what you'll get back:

`js
var expectObj = {
url: 'https://plus.google.com/102817283354809142195/posts/F97fqZwJESL',
object: {
content:
'A picture... of a space ship... launched from earth 40 years ago.',
attachments: [
{
url: 'http://apod.nasa.gov/apod/ap110908.html'
}
]
}
};
`

Let's test that:

`js
var mask = require('json-mask');
var assert = require('assert');

var maskedObj = mask(originalObj, fields);
assert.deepEqual(maskedObj, expectObj);
`

$3

It is also possible to get keys that contain ,*()/ using \ (backslash) as escape character.

`json
{
"metadata": {
"labels": {
"app.kubernetes.io/name": "mysql",
"location": "WH1"
}
}
}
`

You can filter out the location property by metadata(labels(app.kubernetes.io\/name)) mask.

NOTE: In JavaScript String you must escape backslash with another backslash:
`js
var fields = 'metadata(labels(app.kubernetes.io\\/name))'
`

$3

Here's an example of using json-mask to implement the
Google API Partial Response

`js
var http = require('http');
var url = require('url');
var mask = require('json-mask');
var server;

server = http.createServer(function(req, res) {
var fields = url.parse(req.url, true).query.fields;
var data = {
firstName: 'Mohandas',
lastName: 'Gandhi',
aliases: [
{
firstName: 'Mahatma',
lastName: 'Gandhi'
},
{
firstName: 'Bapu'
}
]
};
res.writeHead(200, { 'Content-Type': 'application/json' });
res.end(JSON.stringify(mask(data, fields)));
});

server.listen(4000);
`

Let's test it:

`bash
$ 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: a few more examples are in the /example folder.

Command Line Interface - CLI

When installed globally using npm i -g json-mask you can use it like:

json-mask "" [

]

$3

Stream from online resource:

curl https://api.myjson.com/bins/krrxw | json-mask "url,object(content,attachments/url)"

Read from file and write to output file:

json-mask "url,object(content,attachments/url)" input.json > output.json

Read from file and print redirect to file:

json-mask "url,object(content,attachments/url)" input.json > output.json

CDN

unpkg

- https://unpkg.com/json-mask/build/jsonMask.js
- https://unpkg.com/json-mask/build/jsonMask.min.js`

License

MIT