handleMouseDown (dir, isFirst) {
    if (dir === 'up') {
      this.incrementHold = true
      !isFirst && this.increment()

      setTimeout(
        () => {
          if (this.incrementHold) {
            this.handleMouseDown(dir, false)
          }
        },
        isFirst ? 500 : 50
      )
    } else if (dir === 'down') {
      this.decrementHold = true
      !isFirst && this.decrement()

      setTimeout(
        () => {
          if (this.decrementHold) {
            this.handleMouseDown(dir, false)
          }
        },
        isFirst ? 500 : 50
      )
    }
  }
@function handleMouseDown
@param {string} dir
@param {boolean} isFirst
@returns {void}
Increment/Decrement on mouse held down, if its the first call add a delay before starting