selectn

selectn

Resolves deeply-nested object properties via dot or bracket-notation for Node.js and the browser.

So you can do:

selectn('info.name.full', person);

instead of:

person && person.info && person.info.name && person.info.name.full

Features

• Resolves deeply-nested object properties including dashed (-) keys and arrays.
• Assists in avoiding if (obj && obj.a && obj.a.b && obj.a.b.c) { return obj.a.b.c; }.
• Assists in avoiding Cannot read property '...' of undefined TypeError.
• Supports multiple levels of array nesting (i.e. group[0].section.a.seat[3]).
• Supports dashed key access (i.e. stats.temperature-today).
• selectn is a curried function; thus, partial application is also supported.
• Functions generated by selectn can be passed to higher-order functions like map or filter.
• ES3, ES5, CommonJS, AMD, and legacy-global compatible.

Non-Features

• No eval or Function (see: eval in disguise).
• No typeof since, typeof is not a real solution to this problem but can appear to be due to the way the global scope is implied.

Installation

component

$ component install wilmoore/selectn

bower

$ bower install selectn

npm

volo

$ volo add wilmoore/selectn

manual

1. download

    % curl -#O https://raw.github.com/wilmoore/selectn/master/selectn.js
   

2. use

    <script src="selectn.js"></script>
   

Examples

• Nested property access
• Avoid TypeError
• Dashed keys
• Iterator
• Predicate
• Callback

Nested property access

Given the following object:

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

Apply the selectn function to the path and object parameters for error-free access to deeply nested properties.

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

Avoid TypeError

Avoid the dreaded Cannot read property '...' of undefined TypeError. Instead, selectn will return undefined.

function getName(talk) {
  // NOTE: as called below, `talk` is `undefined`
  return selectn('info.name', talk);
}

getName();
//=> undefined

Dashed keys

Given the following object:

var talk = {
  info: { 'attendee-count': 200 }
};

Apply the selectn function to the path and object parameters for error-free access to deeply nested properties.

selectn('info.attendee-count', talk);
// => 200

Iterator

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

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

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:

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

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

While this example assumes a promises API, this is applicable with any API which takes a function and returns the result of applying that function.

Inspiration

• to-function
• reach

Alternatives

• dref
• path-lookup

License

MIT

Changelog

0.10.0 - 2015-09-08

Changed

• accepts an array of properties.
• better support for accessing falsy primitive values.
• added bower configuration allowing bower installer to work.