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This module uses node-fibers to transform asynchronous functions into synchronous ones. This is designed to work with asynchronous functions following the standard ('done' callback as the last arg).

The main commands are:

  • MakeSync to synchronize a function or object.
  • Sync to start a sync environment (starts a fiber).

When applied to an object, MakeSync patches all the object methods by default. It is also possible to pass some options to be more specific.

The following modes may be used to to make function synchronous (see description further down):

  • sync (default)
  • async
  • mixed-args (default 'mixed')
  • mixed-fibers


npm install make-sync

usage (coffeescript)

simple example

{SyncMakeSync} = require 'make-sync'
= (a,b,done) ->
  res = a+b
  done nullres
# making synchronous  
= MakeSync f
# sync call 
Sync ->
  res = f 12
  console.log "sync ->"res 
obj = 
  f: (a,b,done) ->
    res = a+b
    done nullres
# making synchronous 
MakeSync obj
# sync call   
Sync ->
  res = obj.12
  console.log "obj sync ->"res   


sync (default)

= MakeSync f
# or 
= MakeSync fmode:'sync'

This mode assumes that the function is always called in sync mode within a fiber, so that the 'done' callback is never there. (ie if there is a function at the end it will assume this is a function argument and add it own callback)


= MakeSync fmode:'async'

This mode assumes that the function is always called in asynchronous mode, so doesn't change the function behavior. (probably not useful in most case)

mixed-args (default mixed)

= MakeSync fmode:'mixed'
# or 
= MakeSync fmode:['mixed''args']

This mode uses the function arguments to determine wether it needs to be called synchronously or asynchronously. When the last argument is a function, MakeSync assume the last argument is the 'done' callback. There may be some issues when using other function arguments. Please refer to the section below.

fixed numbers of args / function arguments

This only applies when using the mixed-args mode and calling the function synchronously.

There are 2 strategies to resolve the confusion between the 'done' callback and other function argument, when those are passed at the end of the argument list:

  • use undefined as the last argument
  • pass the number of arguments expected (excluding the callback) to MakeSync.
{SyncMakeSync} = require 'make-sync'
= (a,b, _g, done) ->
  res = a + b + _g()
  done nullres
= -> 10
# synchronizing (not using a fixed number of arg)   
f1 = MakeSync fmode:['mixed''args']
Sync ->
  try f1 12catch error 
    console.log "f1 throws" # thinks that g is the callback 
  res = f1 12gundefined # ok when passing undefined at the end  
  console.log "f1 sync ->"res 
# passing a fixed number of args  
f2 = MakeSync f{mode:['mixed','args']num_of_args: 3}
Sync ->
  res = f2 12# it works  
  console.log "f2 sync ->"res 


= MakeSync fmode:['mixed','fibers']

When using this mode, MakeSync checks wether a fiber is currently available, using 'Fiber.current', and uses the sync or async mode accordingly.

return and error handling in sync mode

This can be configured using the sync-return option.

argument matcher

Argument matchers works like the coffeescript arguments with splats. MakeSync will match the arguments passed to the callback using this pattern. If err is defined it will throw it, otherwise res will be returned. (When using splats on res, res becomes an array)

{SyncMakeSync} = require 'make-sync'
# err + res  
= (done) -> done null'A'
syncF = MakeSync f'sync-return': 'err,res'
Sync ->
  console.log syncF()
# single res  
= (done) -> done 'B'
syncF = MakeSync f'sync-return': 'res'
Sync ->
  console.log syncF()
# return error + res array  
= (done) -> done null'C1''C2' 
syncF = MakeSync f'sync-return': 'err, res...'
Sync ->
  console.log syncF()
# res array  
= (done) -> done 'D1''D2' 
syncF = MakeSync f'sync-return': 'res...'
Sync ->
  console.log syncF()
# the second result only 
= (done) -> done 'E1''E2' 'E3'
syncF = MakeSync f'sync-return': 'ignoreFirst, res, ignoreLast...'
Sync ->
  console.log syncF()


If matchers are not sufficient, you may use a function instead. This function will receive the same arguments as the callback, and its return will be the final result returned.

{SyncMakeSync} = require 'make-sync'
= (done) -> done null1020
options = 
  'sync-return': (err,res1,res2) -> res1 + res2
syncF = MakeSync foptions 
Sync ->
  console.log syncF()


If not specified, this options is defaulted to:

{'sync-return': 'err,res'}

This means that MakeSync expect the function to pass an error, and one result to the callback. It will ignore everything else.

options when calling on objects

When calling MakeSync on an object, MakeSync is called on all its methods.

It is possible to configure the following:

  • inclusion and exclusion lists (per method basis)
  • num_of_args (per method basis)
  • sync-return (per method basis)
  • MakeSync mode (globally)
{SyncMakeSync} = require 'make-sync'
= -> 10
# all the function are included by default,  
# then some are specifically excluded. 
# sync return is set per-function 
obj = 
  f1: (done) -> done null1
  f2: (done) -> done null2
  _f: (done) -> done 3
  f3: (_g, done) -> done null4 + _g()
  f4: (_g, done) -> done 5 + _g()
  f5: (done) -> done null2
options =
  mode: ['mixed''args']
  exclude: ['f1'/^_/]
    '*': 'err,res'
    _f: 'res'
    f4: 'res'
    f5: (err,res) -> res + 1
MakeSync objoptions
Sync ->
  try obj.f1() catch error then console.log "f1 throws" # f1 was excluded   
  console.log 'f2 returns'obj.f2() # OK, not in the exclude list 
  try obj._f() catch error then console.log "_f throws" # _f was excluded 
  try obj.f3 g catch error 
    console.log "f3 throws" # num_of_args not set  
  console.log 'f4 returns'obj.f4 g # OK, num_of_args was set 
  console.log 'f5 returns'obj.f5() # uses sync return function 
# all the function are excluded  
# then some are specifically included. 
obj = 
  f1: (done) -> done 1
  f2: (done) -> done 2
  _f: (done) -> done 3
  f3: (_g, done) -> done 4 + _g()
  f4: (_g, done) -> done 5 + _g()
  f5: (done) -> done 2
options = 
  mode: 'sync'
  exclude: '*'
  include: ['f1''f3']
  'sync-return': 'res' # err is never pass to the done callback 
MakeSync objoptions
Sync ->
  console.log '\nf1 returns'obj.f1() # OK, f1 was included 
  try obj.f2() catch error then console.log "f2 throws" # f2 was excluded 
  console.log 'f3 returns'obj.f3 g # OK, f3 was included 
# exclude can also accept a simple string or a regex 
options1 = exclude: 'f1'
options2 = exclude: /^_/