selectn

selectn

N-levels deep object access via dot/bracket-notation property access string allowing you to type selectn('info.name.full') instead of obj && obj.info && obj.info.name &&, ∞.

Features

• Avoids if (obj && obj.a && obj.a.b && obj.a.b.c) { return obj.a.b.c; }.
• Partial application supported.
• Functions generated by selectn can be passed to applicative functors like Array.prototype.map and Array.prototype.filter.
• Works where typeof fails (i.e. deeply nested properties).
• ES5 and non-ES5 compatible.
• CommonJS, AMD, and legacy-global compatible.
• Provides access to global object if no object reference is given.

Non-Features

• No eval and friends.

Installation

component

$ component install wilmoore/selectn

bower

$ bower install selectn

npm

$ npm install selectn

Example (immediate access)

Given the following object:

var talk = {
  info: { name: 'Go Ahead, Make a Mess' }
};

The generated function can be immediately invoked for error-free and immediate access to deeply nested properties.

selectn('info.name', talk);
// => 'Go Ahead, Make a Mess'

Iterator Example

Given the following list:

var talks  = [
  { info: { name: 'Go Ahead, Make a Mess' }},
  { info: { name: 'Silex Anatomy' }},
  { info: { name: 'Unit Testing in Python' }},
  { info: { name: 'Setting the Stage' }}
];

The generated function can be used as a predicate for map:

var query = selectn('info.name');
//=> [Function]

talks.map(query);
// => [ 'Go Ahead, Make a Mess', 'Silex Anatomy', 'Unit Testing in Python', 'Setting the Stage' ]

Predicate Example

Given the following object of language strings:

var language = [
  { strings: { en: { name: 'english' } }},
  { strings: { es: { name: 'spanish' } }},
  { strings: { km: { name: 'khmer'   } }},
  { strings: { es: { name: 'spanish' } }},
];

The generated function can be used as a predicate for filter:

var spanish = selectn('strings.es');
//=> [Function]

language.filter(spanish).length;
//=> 2

Callback Example

You expect the following JSON data from an XMLHttpRequest:

var data = { Client: { Message: { id: d50afb80-a6be-11e2-9e96-0800200c9a66 } } };

Access the Client.Message.id property and log the result to the console (using promises):

$.ajax({...})
  .then(selectn('Client.Message.id'))
  .then(console.log.bind(console));

//=> d50afb80-a6be-11e2-9e96-0800200c9a66

NOTE: Even if you don't use this methodology in production code, it can be a handy timesaver in terms of quick debugging.

Rationale

In larger, data-driven applications, there tends to be a need to do a lot of deep object access which can quickly lead to code like this:

var name;

if (contact && contact.info && contact.info.name) {
  name = contact.info.name.full || 'unknown';
}

The following is much more concise:

var name = selectn('info.name.full')(contact) || 'unknown';

Neckbeard Info

In case you care about this sort of thing, we are able to do normal function application as well as partially apply when that is convenient due to currying.

• selectn('info.name.full', contact) (normal function application)
• selectn('info.name.full')(contact) (partial application without a partial helper like Function.prototype.bind)

Since selectn is a 2-ary function, we don't need to use an external library for currying as the algorithm is simple.

Alternatives

• You can use typeof; however, typeof only "appears" to work due to the way the global scope is implied.
• Other solutions involve eval and/or Function (eval in disguise).

Inspiration

• to-function
• reach
• dref

License

MIT