code: function Sustained (obs, timeThreshold, checkUpdateImmediately) {
    var outputValue = Value(obs())
    var lastValue = null
    var timer = null
  
    return computed(outputValue, v => v, {
      onListen: () => watch(obs, onChange)
    })
  
    function onChange (value) {
      if (checkUpdateImmediately && checkUpdateImmediately(value)) {
        clearTimeout(timer)
        update()
      } else if (value !== lastValue) {
        clearTimeout(timer)
        var delay = typeof timeThreshold === 'function' ? timeThreshold(value, outputValue()) : timeThreshold
        timer = setTimeout(update, delay)
      }
      lastValue = value
    }
  
    function update () {
      var value = obs()
      if (value !== outputValue()) {
        outputValue.set(value)
      }
    }
  }
docs: only broadcast value changes once a truthy value has stayed constant for more than timeThreshold