wilmooreselectn
Curried property accessor function that resolves deeply-nested object properties via dot/bracket-notation string path while mitigating
TypeErrorsvia friendly and composable API.
yarn add selectnor
npm install selectn --saveor
<script src="https://unpkg.com/selectn/selectn.min.js"></script>Overview
allows you to refactor this:
person && person.info && person.info.name && person.info.name.fullinto:
selectn('info.name.full', person)or refactor this:
contacts.map(function (contact) {
return contact && contact.addresses && contact.addresses[0]
})into:
contacts.map(selectn('addresses[0]')))Demo
Features
- Mitigate boilerplate guards like
if (obj && obj.a && obj.a.b && obj.a.b.c). - Mitigate TypeError
Cannot read property '...' of undefined. - Multiple levels of array nesting:
'group[0].section.a.seat[3]'. - Dashed key access:
'stats.temperature-today'. - When the value at the given path is a function, it is invoked and the functions returned value is returned.
selectnis auto-curried so partial application is automatic when you omit the second argument.selectnuses Haskell style parameter order (AKA: data-last) which enables pointfree style programming.- Functions returned by
selectnare higher-order property accessors which can be passed to other higher-order functions like map or filter. - Compatible with modern and legacy browsers, Node/CommonJS, and AMD.
Non-Features
- No eval or Function (see:
evalin 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.
Usage example(s)
property accessor as predicate
Avoid annoying Cannot read property '...' of undefined
TypeErrorwithout writing boilerplate anonymous functions or guards.
var selectn = require('selectn')
var language = [
{ strings: { en: { name: 'english' } }},
{ strings: { es: { name: 'spanish' } }},
{ strings: { km: { name: 'khmer' } }},
{ strings: { es: { name: 'spanish' } }},
{ nodatas: {}}
]
var spanish = selectn('strings.es')
//=> [Function]
language.filter(spanish).length
//=> 2point-free property accessor
Access deeply nested properties (including dashed properties) using point-free style.
var selectn = require('selectn')
var data = {
client: {
message: { 'message-id': 'd50afb80-a6be-11e2-9e96-0800200c9a66' }
}
}
var getId = selectn('client.message.message-id')
//=> [Function]
Promise.resolve(data).then(getId)
//=> 'd50afb80-a6be-11e2-9e96-0800200c9a66'property accessor for functor
Avoid wrapping property accessors in anonymous functions.
var selectn = require('selectn')
var contacts = [
{ addresses: [ '123 Main St, Broomfield, CO 80020', '123 Main St, Denver, CO 80202' ] },
{ addresses: [ '123 Main St, Kirkland, IL 60146' ] },
{ phones: [] },
]
var primaryAddress = selectn('addresses[0]')
//=> [Function]
contacts.map(primaryAddress)
//=> [ '123 Main St, Broomfield, CO 80020', '123 Main St, Kirkland, IL 60146', undefined ]support for keys containing .
Pass an array as path instead of a string.
var selectn = require('selectn')
var data = {
client: {
'message.id': 'd50afb80-a6be-11e2-9e96-0800200c9a66'
}
}
selectn(['client', 'message.id'], data)
//=> 'd50afb80-a6be-11e2-9e96-0800200c9a66'value at path is a function
Avoid
var fn = data.may.be.a.fn; if (typeof fn === 'function') fn().
var selectn = require('selectn')
function hi () { return 'hi' }
var data = { may: { be: { a: { fn: hi } } } }
selectn('may.be.a.fn', data)
//=> 'hi'API (partial application)
selectn(String|Array)
arguments
path (String|Array)Dot/bracket-notation string path or array.
returns
(Function)Unary function accepting the object to access.
API (full application)
selectn(String|Array, Object)
arguments
path (String|Array)Dot/bracket-notation string path or array.object (String|Array)Object to access.
returns
(*|undefined)Value at path if path exists orundefinedif path does not exist.
Other Languages
selectn has inspired ports to other languages:
| Language | Project |
|---|---|
| Python | selectn |
Related
Other JS packages whose friendly API is driven by selectn:
Inspiration
JS packages that have inspired selectn:
Alternatives
Alternative packages you might like instead of selectn:
Licenses
