readme.md

kget

Uses one or more keys to retrieve a value from a Map, Object, or other collection. Supports nesting, loose key matching, and more.

Installation

Requires Node.js 8.3.0 or above.

npm i kget

API

The module exports a function (get()) that has other functions attached to it as methods (e.g. get.any()).

get()

Parameters

1. Bindable: collection (Array, iterator, Map, Object, Set, string, Typed Array, or WeakMap): The key-value collection from which to retrieve a value.
2. keychain (any, or array of any): A key to retrieve, or an array of nested keys.
3. Optional: Object argument:
   • arrays / maps / sets / weakMaps (arrays of classes/strings): Arrays of classes and/or string names of classes that should be treated as equivalent to Array/Map/Set/WeakMap (respectively).
   • elseReturn (any): A value to return if keychain is an invalid reference. Only takes effect if no elseThrow is specified. Defaults to undefined.
   • elseThrow (Error or string): An error to be thrown if keychain is an invalid reference. A string will be wrapped in an Error object automatically.
   • get (function): A callback which, if provided, will override the built-in code that fetches an individual key from a collection. Use this if you need to support collections whose custom APIs preclude the use of parameters like maps. The callback will be called with five arguments: the collection, the key, the options object, the fallback to return if the key is not found, and a callback for the built-in get behavior (to which your custom get callback can defer if it determines that it doesn’t need to override the default behavior after all).
   • inObj (boolean): Whether or not to search inherited properties if collection is an Object (i.e. not another recognized type). Defaults to false.
   • loose (boolean): Whether or not to evaluate keys loosely (as defined by looselyEquals). Defaults to false.
   • looselyEquals (function): A callback that accepts two values and returns true if they are to be considered equivalent or false otherwise. This argument is only used if loose is true. If this option is omitted, then the equals module is used. This module will, among other things, consider arrays/objects to be equal if they have the same entries.
   • numerifyIndexes (boolean): Set to true to convert number-containing key strings to numbers. This is most useful when the split option is enabled: if you use split to divide a 'key.0' keychain into 'key' and '0', enabling this option will result in the '0' key being converted to a numeric 0 index. Defaults to false.
   • preferStrict (boolean): Only applies if loose is true. If true, then strictly-identical keys will be preferred over loosely-equivalent keys. Otherwise, the first loosely-equivalent key found will be used, even if a strictly-identical one comes later. Defaults to false.
   • reverse (boolean): Set to true to use the last matching key instead of the first one. Only applies if loose is true. Defaults to false.
   • split (boolean or object): Set to true to parse dot-separated keychain strings (e.g. 'key1.key2') as separate keys. You can also provide an object of options to be forwarded to the split-string module. Defaults to false.

Return Values

• Returns the value from collection referenced by keychain.
• If no such value is found, returns elseReturn if set.
• Otherwise returns undefined.

Example

In the following example, kget fetches a map key, then an object key, then a string index:

const get = require('kget')

const map = new Map()
map.set('mapKey', {objKey: 'string'})

get(map, ['mapKey', 'objKey', 5]) // 'g'

get.any()

Has the same signature as the main function, except that the second parameter is called keychains and expects an array of keys or keychain arrays to be tried one-by-one until one of them points to a value.

Example

const get = require('kget')

get.any({c: 3, d: 4}, [['a', 'subkey'], 'b', 'c']) // 3

The function tries the keys a.subkey, b, and c in order. The first key found (c) has its value returned.

get.in()

This method is an alias for calling the main get() method with the inObj option set to true.

get.any.in()

This method is an alias for calling get.any() with the inObj option set to true.

get.key()

This method allows you to determine the key that would be retrieved when loose equivalence is used.

Parameters

1. Bindable: collection (Array, iterator, Map, Object, Set, string, or Typed Array): The key-value collection from which to retrieve a value.
2. key (any): A key which may or may not exist in collection. (This can only be a single key, not a key chain.)
3. Optional: Object argument: The same options as in the base get() function.

Return Values

• If key exists in collection:
  • If loose is set to true in the options argument, the first key in collection that is loosely equal to key will be returned.
  • Otherwise, key is returned as-is.
• If key does not exist in collection, the return value is undefined.

Example

const get = require('kget')

const a = ['key']
const b = ['key']

const map = new Map()
map.set(a, 'value a')
map.set(b, 'value b')

get(map, b) // 'value b'
get(map, b, {loose: true}) // 'value a'

get.key(map, b) === b // true
get.key(map, b, {loose: true}) === a // true

get.entry()

Parameters

1. Bindable: collection (Array, iterator, Map, Object, Set, string, or Typed Array): The key-value collection from which to retrieve a value.
2. key (any): A key which may or may not exist in collection. (This can only be a single key, not a key chain.)
3. Optional: Object argument: Any of (as defined above): arrays, maps, sets, weakMaps, elseReturn, elseThrow, inObj, loose, looselyEquals, and preferStrict.

Return Values

• If the key is found, returns a two-element array containing the matched key and the retrieved value.
• If the key is not found, returns elseReturn if provided, otherwise undefined.

Related

The “k” family of modules works on keyed/indexed collections.

• khas
• kedit
• kset
• kinc
• kdel

The “v” family of modules works on any collection of values.

• vhas
• vget
• vsize
• vadd
• vdel