Debounce a function, with the option to accumulate args

accumulatedDebounce.js

export function debounce(delay, callback, accumulateData) {
  let timeout = null
  let data = []
  return function () {
    if (accumulateData) {
      const arr = []
      for (let i = 0; i < arguments.length; ++i) {
        arr.push(arguments[i])
      }
      data.push(arr)
    }
    if (timeout) {
      clearTimeout(timeout)
    }
    const args = arguments
    timeout = setTimeout(function () {
      callback.apply((accumulateData) ? { data } : null, args)
      data = []
      timeout = null
    }, delay)
  }
}


// Unit tests should illustrate pretty well what this function does...

import { debounce } from '../../../src/util'


jest.useFakeTimers()

describe('util', () => {
  describe('debounce', () => {
    it('debounces the function', () => {
      const target = jest.fn()
      const func = function(int) {
        target(int)
      }
      const debouncedFunc = debounce(1000, func, false)

      debouncedFunc(1)
      debouncedFunc(2)
      debouncedFunc(3)
      jest.runAllTimers()

      expect(target).toHaveBeenCalledTimes(1)
      expect(target).toHaveBeenCalledWith(3)
    })

    it('debounces the function and accumulates args', () => {
      const target = jest.fn()
      const func = function(int) {
        target(this.data)
      }
      const debouncedFunc = debounce(1000, func, true)

      debouncedFunc(1)
      debouncedFunc(2)
      debouncedFunc(3)
      jest.runAllTimers()
      debouncedFunc(4)
      jest.runAllTimers()

      expect(target).toHaveBeenCalledTimes(2)
      expect(target.mock.calls[0][0]).toEqual([[ 1 ], [ 2 ], [ 3 ]])
      expect(target.mock.calls[1][0]).toEqual([[ 4 ]])
    })
  })
})