Problem description

The error message is as follows:

TS2769: No overload matches this call.
  Overload 1 of 2, '(type: "*", handler: WildcardHandler<Record<EventType, unknown>>): void', gave the following error.
    Argument of type '"form-item-created"' is not assignable to parameter of type '"*"'.
  Overload 2 of 2, '(type: "form-item-created", handler?: Handler<unknown> | undefined): void', gave the following error.
    Argument of type '(func: ValidateFunc) => void' is not assignable to parameter of type 'Handler<unknown>'.
    47 |     onUnmounted(() => {
    48 |       
  > 49 |       emitter.off('form-item-created', callback)
       |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    50 |       funcArr = []
    51 |     })
    52 |

reason:

Mitt’s definition file has been upgraded

Solution:

Code before modification

import mitt from 'mitt'

type ValidateFunc = () => boolean
export const emitter = mitt()

emitter.emit('formItemCreated', validateInput)

  const callback = (func: ValidateFunc) => {
    funcArr.push(func)
  }
  emitter.on('formItemCreated', callback)
  onUnmounted(() => {
    emitter.off('formItemCreated', callback)
    funcArr = []
  })

Modified code

import mitt from 'mitt'

type ValidateFunc = () => boolean

export const emitter = mitt<{
  formItemCreated: ValidateFunc
}>()
    ...

Or use the following code

import mitt from 'mitt'

type ValidateFunc = () => boolean

type Emits<EventType extends string | symbol, T> = {
  on(type: EventType, handler: (arg: T) => void): void
  off(type: EventType, handler: (arg: T) => void): void
  emit(type: EventType, arg: T): void
}

// type Emitter = Emits<'a', number> & Emits<'b', string>;
type Emitter = Emits<'form-item-created', ValidateFunc>

export const emitter: Emitter = mitt<Emitter>()

    ...