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Monadic - JavaScript micro library

Very simple library that, I think implement a monad in Javascript and add some funtionaly to functions that belong to orignal object wraped by Monadic Monad.

Functions wraped by Monadic, are automaticaly chainable if they don't return a value. Functions are executed in the context of orignal object. Functions that modify an object modify local copy of that object that can be retrieve at the end of monadic chain.


Monadic function wrap you original object and add new methods add and get

  • add - append new function to monad
  • get - return original object

var o = {
    baz: 2,
    foo: function(a) {
        this.baz += a;
    bar: function(a) {
        this.baz = a * a;

Monadic(o).bar(10).foo(10).add('baz', function() {
    this.baz += 10;
    return this;

you will get 120. In orignal o object baz will still equal 2.

Add function to Object prototype

You can add monadic method to Object prototype using:


so all objects will have monadic method that will create Monadic Monad from that object.

Monadic Functions API

Your wrapped functions inside Monadic have these methods (methods that accept a function will return new function to get monadic object you need to call self).

  • before(function) - value from your before function is is passed to original function
  • after(function) - argument to your after function is the value of returned by original function
  • limit(number) - make a function accept only fixed number of arguments (more arguments are ignored)
  • self() - return monadic object
  • when(function) - if function return false the origal function is not executed

You can chain these methods

console = console.monadic({monad: false}).log.when(function() {
    if (!debug) {
        return false;
}).log.before(function(str) {
   if (str.match(/LOG/)) {
      // save log in the file
   return str;

When you pass false to monadic method it will keep context of orignal object, it will not create new object each time you call a method (it will not be real Monad then), so you can pass log as callback.

[1,2,3,4].forEach(console.monadic({monad: false}).log.limit(1));

In this example foo function is modified after it return it's value so foo is always returning 10. Argument to after function is a value returned by a function.

Monadic({ foo: function(a) { return 10/a; } }).foo.before(function(a) {
    if (a == 0) {
        throw 'You should not divide by 0, you know';
    } else {
        return a;

NOTE: fuction methods are not creating new Monad so they modify original, current Monad object


Copyright (C) 2012 Jakub Jankiewicz <>

Licensed under GNU GPL Version 3 license

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