backing-off.coffee

backing-off.coffee

# Re-try function with exponential back-off time
# `max`: Maximum amount of attempts
# `wait`: Wait time between attemps, in milliseconds
# `attempt`: Function to make one attempt, accepts arguments <nth try>, <callback upon success>

gently = @gently = (max, wait, attempt) ->
  new Promise (fulfill, fail) ->
    recur = (max, wait, attempt, n) ->
      pending = setTimeout (->
        if n is max
          clearTimeout pending
          fail n

        else recur max, 2*wait, attempt, n+1
      ), wait
      attempt n, ->
        clearTimeout pending
        fulfill n

    recur max, wait, attempt, 1

@tryit = (attempts) ->
  attempt = (n, done) ->
    if n is attempts then done()
    else console.log "My hypothetical request no #{n}..."
  # Try it maximum 4 times with initial wait time of 130ms:
  gently(4, 130, attempt).then(
    ((n) -> console.log "  ..succeeded on attempt #{n}"),
    ((n) -> console.log "  ..failed after attempt #{n}") )