Good
Afternoon

Is mise
Cory Brown

employed @ nav

I am happy to be here

JS default values

JS default values

const someFn = ({
  doStuffForActiveItems = id,
  config = {},
  list = [],
  delimiter = ''
} = {}) => 
  list
    .filter(({ isActive = false }) => isActive)
    .map((item = {}) => 
      doStuffForActiveItems({...config, ...item})
    )
    .map(({ name = ''}) => name)
    .join(delimiter)
const someFn = ({
  doStuffForActiveItems,
  config,
  list,
  delimiter,
}) => {
  if (Array.isArray(list)) {
    const names =  list
      .filter(({ isActive }) => isActive)
      .map((item) => {
        const item = item || {}
        if (
          _.isPlainObject(config) &&
          _.isPlainObject(item) &&
          typeof doStuffForActiveItems === 'function'
        ) {
          return doStuffForActiveItems({...config, ...item})          
        }
      })
      .map(({ name }) => {
        name = name || ''
        return name
      })
    
    if (typeof delimeter !== 'string') {
      delimeter = ''
    }
    return name.join(delimiter)
  } else {
    return ''
  }
}
  

We ❀️ JS default values

What value do we make
the default?
πŸ€”

Like a placeholder?

const gimme1stThingName = (things = [{ name: 'thing name' }]) => {
  const [first = { name: 'first thing name ' }] = things
  return first.name
}

With the most likely value?

const gimme1stThingName = (things = [{ name: 'Boaty McBoatface' }]) => {
  const [first = { name: 'Boaty McBoatface' }] = things
  return first.name
}

Throw an error?

const gimme1stThingName = (things = missingArg(`Y U No giv things?`)) => {
  const [first = missingArg(`Y things empty?`)] = things
  return first.name
}
const missingArg = (message) => { throw new Error(message) }

πŸ€·πŸΌβ€β™€οΈ

Monoidal
Identity
Elements

Β 

πŸŽ™πŸ’§

You're Welcome!

?

Β What
the fork
is that?

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Monoidal
Identity
Elements

Monoid

An algebraic structure with a single associative binary operation and an identity element

Monoid

An algebraic structure with a single associative binary operation and an identity element

Monoid

An algebraic structure with a single associative binary operation and an identity element

Monoid

An algebraic structure with a single associative binary operation and an identity element

Monoid

  1. A data type (String, Number, Array, etc.)
    Β 
  2. An associative, binary operator (concat)
    Β 
  3. An element with left and right identity

Number

+
-
*
/
N + i
i + N
=
N
=
i = 0
N * i
i * N
=
N
=
i = 1

Object to hold fragment

Monoid #1

Type: Number
Operator: addition (+)
Identity Element: 0

Monoid #2

Type: Number
Operator: multiplication (*)
Identity Element: 1

String

+
`${x}${y}`
''.concat
S + i = i + S = S
i = ''
`${S}${i}` = `${i}${S}` = S
S.concat(i) = i.concat(S) = S

Monoid #3

Type: String
Operator: concat (+, `${}${}`, ''.concat)
Identity Element: ''

Boolean

&&
||
B && i = i && B = B
i = true
B || i = i || B = B
i = false

Monoid #4

Type: Boolean
Operator: &&
Identity Element: true

Monoid #5

Type: Boolean
Operator: ||
Identity Element: false

Array

[].concat
[...]
A.concat(i) = i.concat(A) = A
i = []
[...A, ...i] = [...i, ...A] = A

Monoid #6

Type: Array
Operator: concat, [...]
Identity Element:[]

Object

Object.assign
{...}
Object.assign(O, i) = Object.assign(i, O) = O
i = {}
{...O, ...i} = {...i, ...O} = O

Monoid #7

Type: Object
Operator: merge (Object.assign, {...})
Identity Element: {}

Function

πŸ€”
F πŸ€” i = i πŸ€” F = F
i = πŸ€·β€β™€οΈ

Function

Just a

const compose = (...fns) => (data) => fns.reduceRight((result, fn) => fn(result), data)
compose
compose(F, i) = compose(i, F) = F
i = πŸ€·β€β™€οΈ
i = (x) => x

Monoid #8

Type: Function
Operator: compose
Identity Element: (x) => x

const someFn = ({
  doStuffForActiveItems = id, /* <- monoidal identity element */
  config = {}, /* <- monoidal identity element */
  list = [], /* <- monoidal identity element */
  delimiter = '' /* <- monoidal identity element */
} = {} /* <- monoidal identity element */) => 
  list
    .filter(({ isActive = false }) => isActive)
    .map((item = {} /* <- monoidal identity element */) => 
      doStuffForActiveItems({...config, ...item})
    )
    .map(({ name = '' /* <- monoidal identity element */}) => name)
    .join(delimiter)

Tapadh leibh

p.s. Nav is hiring. Come talk to me. 😁

Monodial Identity Elements

By Cory Brown

Monodial Identity Elements

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