throttleUpload (rate) {
    rate = Number(rate)
    if (isNaN(rate) || !isFinite(rate) || rate < -1) return false
    this._uploadLimit = rate
    if (this._uploadLimit < 0) return this.throttleGroups.up.setEnabled(false)
    this.throttleGroups.up.setEnabled(true)
    this.throttleGroups.up.setRate(this._uploadLimit)
  }
Set global upload throttle rate
@param  {Number} rate (must be bigger or equal than zero, or -1 to disable throttling)