# Method Concurrent.Future()->on_success()

Method on_success

  ``this_program` on_success(`function`(`mixed`, `mixed` ... :`void`) `cb`, `mixed` ... `extra`)`

Description

  Register a callback that is to be called on fulfillment.

Parameter `cb`

  Function to be called. The first argument will be the result of the Future.

Parameter `extra`

  Any extra context needed for `cb`. They will be provided as arguments two and onwards when `cb` is called.

Note

  `cb` will always be called from the main backend.

See also

  on_failure()