CFP - Docs - returnUndefined

returnUndefined

```
() => undefined
```

Return undefined

returnUndefined() // is undefined
returnUndefined('a', 'b') // is undefined
returnUndefined() // is undefined

Try It

returnUndefined() // is undefined
returnUndefined('a', 'b') // is undefined
returnUndefined() // is undefined

Developers commonly use this as a default. Below, we maintain a keyboard customizer. We only cover one macro key for now, which does nothing by default. Let's have it type 'macro1' to make sure our customizer is working.

Try It

const doNothing = returnUndefined

// keyboard customizer
const initKeyboardConfig = () => {
  const keyboard = {
    macro1: doNothing,
  }

  const cfg = {
    pressMacro1: () => keyboard.macro1(),
    assignMacro1: fn => {
      keyboard.macro1 = fn
    },
    unassignMacro1: () => {
      keyboard.macro1 = doNothing
    },
  }

  return cfg
}

const config = initKeyboardConfig()
const result1 = config.pressMacro1()
console.log(result1) // is undefined

const typeMacro1 = () => 'macro1'
config.assignMacro1(typeMacro1)
const result2 = config.pressMacro1()
console.log(result2) // is 'macro1'

config.unassignMacro1()
const result3 = config.pressMacro1()
console.log(result3) // is undefined
type UnknownFunction = (...args: never[]) => unknown

const doNothing = returnUndefined

// keyboard customizer
const initKeyboardConfig = () => {
  const keyboard: Record<string, UnknownFunction> = {
    macro1: doNothing,
  }

  const cfg = {
    pressMacro1: () => keyboard.macro1(),
    assignMacro1: (fn: UnknownFunction) => {
      keyboard.macro1 = fn
    },
    unassignMacro1: () => {
      keyboard.macro1 = doNothing
    },
  }

  return cfg
}

const config = initKeyboardConfig()
const result1 = config.pressMacro1()
console.log(result1) // is undefined

const typeMacro1 = () => 'macro1'
config.assignMacro1(typeMacro1)
const result2 = config.pressMacro1()
console.log(result2) // is 'macro1'

config.unassignMacro1()
const result3 = config.pressMacro1()
console.log(result3) // is undefined

Try It

const doNothing = returnUndefined

// keyboard customizer
const initKeyboardConfig = () => {
  const keyboard = {
    macro1: doNothing,
  }

  const cfg = {
    pressMacro1: () => keyboard.macro1(),
    assignMacro1: fn => {
      keyboard.macro1 = fn
    },
    unassignMacro1: () => {
      keyboard.macro1 = doNothing
    },
  }

  return cfg
}

const config = initKeyboardConfig()
const result1 = config.pressMacro1()
console.log(result1) // is undefined

const typeMacro1 = () => 'macro1'
config.assignMacro1(typeMacro1)
const result2 = config.pressMacro1()
console.log(result2) // is 'macro1'

config.unassignMacro1()
const result3 = config.pressMacro1()
console.log(result3) // is undefined
type UnknownFunction = (
  ...args: never[]
) => unknown

const doNothing = returnUndefined

// keyboard customizer
const initKeyboardConfig = () => {
  const keyboard: Record<
    string,
    UnknownFunction
  > = {
    macro1: doNothing,
  }

  const cfg = {
    pressMacro1: () => keyboard.macro1(),
    assignMacro1: (fn: UnknownFunction) => {
      keyboard.macro1 = fn
    },
    unassignMacro1: () => {
      keyboard.macro1 = doNothing
    },
  }

  return cfg
}

const config = initKeyboardConfig()
const result1 = config.pressMacro1()
console.log(result1) // is undefined

const typeMacro1 = () => 'macro1'
config.assignMacro1(typeMacro1)
const result2 = config.pressMacro1()
console.log(result2) // is 'macro1'

config.unassignMacro1()
const result3 = config.pressMacro1()
console.log(result3) // is undefined

This function is more commonly known as noop which stands for "no operation." More intuitively, we can think of the function as "do nothing." Typically, you'll see it used in libraries that take a callback, which does nothing by default.