CFP - Docs - mSet

mSet

(key: PropertyKey, value: any) => (anything: any) => anything

Set a property

Consider set instead.
This is for the uncommon case where mutating anything is required.

Try It

const obj = { a: 'b' }
const setAToC = mSet('a', 'c')
const mutatedObj = setAToC(obj)

console.log(mutatedObj === obj) // is true
console.log(obj) // is { a: 'c' }
const obj = { a: 'b' }
const setAToC = mSet('a', 'c')
const mutatedObj = setAToC(obj)

console.log(mutatedObj === obj) // is true
console.log(obj) // is { a: 'c' }

Try It

const obj = { a: 'b' }
const setAToC = mSet('a', 'c')
const mutatedObj = setAToC(obj)

console.log(mutatedObj === obj) // is true
console.log(obj) // is { a: 'c' }
const obj = { a: 'b' }
const setAToC = mSet('a', 'c')
const mutatedObj = setAToC(obj)

console.log(mutatedObj === obj) // is true
console.log(obj) // is { a: 'c' }

Sometimes we want to set a property. Below, we are building an array of cast members for True Detective Season 1. Let's add a property 'isLead' using the set of lead members.

Try It

const topBilledCast = [
  { name: 'Matthew McConaughey' },
  { name: 'Woody Harrelson' },
  { name: 'Michelle Monaghan' },
  { name: 'Michael Potts' },
  { name: 'Tory Kittles' },
]

const flagLead = mSet('isLead', true)
const leads = new Set(['Matthew McConaughey', 'Woody Harrelson'])
const isLead = actor => leads.has(actor.name)
const flagAllLeads = compose([keepWhen(isLead), forEach(flagLead)])
flagAllLeads(topBilledCast)

console.log(topBilledCast)
// is [
//   { name: Matthew McConaughey, isLead: true }
//   { name: Woody Harrelson, isLead: true }
//   { name: Michelle Monaghan }
//   { name: Michael Potts }
//   { name: Tory Kittles }
// ]
type Actor = {
  name: string
  isLead?: true
}
const topBilledCast: Actor[] = [
  { name: 'Matthew McConaughey' },
  { name: 'Woody Harrelson' },
  { name: 'Michelle Monaghan' },
  { name: 'Michael Potts' },
  { name: 'Tory Kittles' },
]

const flagLead = mSet('isLead', true)<Actor>
const leads = new Set(['Matthew McConaughey', 'Woody Harrelson'])
const isLead = (actor: Actor) => leads.has(actor.name)
const flagAllLeads = compose([
  keepWhen(isLead)<Actor[]>,
  forEach(flagLead)<Actor[]>,
])
flagAllLeads(topBilledCast)

console.log(topBilledCast)
// is [
//   { name: Matthew McConaughey, isLead: true }
//   { name: Woody Harrelson, isLead: true }
//   { name: Michelle Monaghan }
//   { name: Michael Potts }
//   { name: Tory Kittles }
// ]

Try It

const topBilledCast = [
  { name: 'Matthew McConaughey' },
  { name: 'Woody Harrelson' },
  { name: 'Michelle Monaghan' },
  { name: 'Michael Potts' },
  { name: 'Tory Kittles' },
]

const flagLead = mSet('isLead', true)
const leads = new Set([
  'Matthew McConaughey',
  'Woody Harrelson',
])
const isLead = actor => leads.has(actor.name)
const flagAllLeads = compose([
  keepWhen(isLead),
  forEach(flagLead),
])
flagAllLeads(topBilledCast)

console.log(topBilledCast)
// is [
//   { name: Matthew McConaughey, isLead: true }
//   { name: Woody Harrelson, isLead: true }
//   { name: Michelle Monaghan }
//   { name: Michael Potts }
//   { name: Tory Kittles }
// ]
type Actor = {
  name: string
  isLead?: true
}
const topBilledCast: Actor[] = [
  { name: 'Matthew McConaughey' },
  { name: 'Woody Harrelson' },
  { name: 'Michelle Monaghan' },
  { name: 'Michael Potts' },
  { name: 'Tory Kittles' },
]

const flagLead = mSet('isLead', true)<Actor>
const leads = new Set([
  'Matthew McConaughey',
  'Woody Harrelson',
])
const isLead = (actor: Actor) =>
  leads.has(actor.name)
const flagAllLeads = compose([
  keepWhen(isLead)<Actor[]>,
  forEach(flagLead)<Actor[]>,
])
flagAllLeads(topBilledCast)

console.log(topBilledCast)
// is [
//   { name: Matthew McConaughey, isLead: true }
//   { name: Woody Harrelson, isLead: true }
//   { name: Michelle Monaghan }
//   { name: Michael Potts }
//   { name: Tory Kittles }
// ]

This utility requires the key be assignable on anything

The example shows the error thrown

Try It

const setAToC = mSet('a', 'c')
try {
  setAToC(1)
} catch (err) {
  console.log(err)
  // prints
  // 'mSet requires key to be assignable.  See error properties for more info.'
}
const setAToC = mSet('a', 'c')
const obj = {}
Object.defineProperty(obj, 'a', {
  enumerable: true,
  writable: false,
  value: 'b',
})
try {
  setAToC(obj)
} catch (err) {
  console.log(err)
  // prints
  // 'mSet requires key to be assignable.  See error properties for more info.'
}

Try It

const setAToC = mSet('a', 'c')
try {
  setAToC(1)
} catch (err) {
  console.log(err)
  // prints
  // 'mSet requires key to be assignable.  See
  // error properties for more info.'
}
const setAToC = mSet('a', 'c')
const obj = {}
Object.defineProperty(obj, 'a', {
  enumerable: true,
  writable: false,
  value: 'b',
})
try {
  setAToC(obj)
} catch (err) {
  console.log(err)
  // prints
  // 'mSet requires key to be assignable.  See
  // error properties for more info.'
}