Utility for easily creating chainable methods and complex fluent APIs in JavaScript
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Chainlang is a utility for easily creating chainable methods and complex fluent APIs in JavaScript.


Fuent APIs make code easier to read and understand. Replacing a large options object parameter with a convenient fluent API can greatly simplify the use of many library functions. In an interactive environment like the nodejs repl, or the Firebug console, programmers can take advantage of auto-completion and exploratory programming to uncover the features of your fluent API without having to resort to the documentation.


Creating a Chainable API

Just pass any JavaScript object to chainlang.create to create a chainable api:

var adder = {
    add: function(val){ 
        this._subject += val; 
    calc: function() { 
        return this._subject; 

var to = chainlang.create(adder);

// Logs: 10

chainlang.create will return a function that starts your chain expression. The optional parameter to this function will be saved in this._subject and accessible by all of your methods. If no value is returned by a method in the chain, the chain object itself is implicitly returned so you may continue to chain other methods.

Everything is Chainable

The object you pass to chainlang.create need not have all of it's method at the root level, as in the example above. Any method on the object graph, no matter how deeply nested, will be chainable.

var even = {
    deeply: {
        nested: {
            methods: function(){
    are: {
        chainable: function(){

var even = chainlang.create(even);

// Logs: true

Skip The Initial Call

As mentioned, chainlang.create returns a function that will start your chain. This function returns the chain object that all of your subsequent method calls are applied to. However, while this is required to allow chaining, the function call is only useful to clients if you want to capture some _subject. So, chainlang will allow you to omit the first function call, and in that case makes it implicitly before the execution of any methods you do call, and the called method is applied to chain as usual.

All that means that instead of


You may write


Saving yourself one massive set of parens.

Using chainlang.append

chainlang.append is a simple function to help you build your language spec before passing it to chainlang.create. With chainlang.append, you can declare leaf nodes of an object graph and have the parent nodes filled in for you. So, the previous example could have been written like this:

var even = {};
chainlang.append(even, 'deeply.nested.methods', function(){ return; });
chainlang.append(even, 'are.chainable', function(){ console.log(true); });
even = chainlang.create(even);

// Logs: true

If you bind chainlang.append to some object, the first parameter may be omitted

var even = {};
var define = chainlang.append.bind(even);

define('deeply.nested.methods', function(){ return; });
define('are.chainable', function(){ console.log(true); });

even = chainlang.create(even);

// Logs: true

Sharing Data Between Links

Along with this._subject, all method calls have access to this._data. this._data is initially empty, and is simply provided as a convenient place to store information between links in a chained expression.

var spec = {};
var define = chainlang.append.bind(spec);

define('setData', function(val){ 
    this._data.field = val; 
define('logData', function(){ 

var chain = chainlang.create(spec);

// Logs: 999

Keeping Your Privates Hidden

Sometimes it's desirable to hide some methods of your chainable api until it makes sense to use them. chainlang provides no built-in support for this, but it is recommended that you simply hide these nodes behind a field with a name like '_private'. That way, programmers using your api will not be tempted to use these methods in a context where it does not make sense to do so. Also, keeping them all behind a field like this, instand of simply prefixing them all with an '_' will prevent the auto-completion results from being cluttered with fields that are supposed to be private in the first place. For example:

var delaySpec = {};
var define = chainlang.append.bind(delaySpec);

define('for', function(count){
    this._data.count = count;

    // exposing our private 'units' object now that we have a count
    return this._private.units;

define('_private.units.seconds.then', function(callback){
    setTimeout(callback, this._data.count * 1000);

define('_private.units.minutes.then', function(callback){
    setTimeout(callback, this._data.count * 1000 * 60)

var delay = chainlang.create(delaySpec);

// After 5 seconds, logs: '5 seconds elapsed'
    console.log('5 seconds elapsed');

// After 5 minutes, logs: '5 minutes elapsed'
    console.log('5 minutes elapsed');

In the previous example, it would not make sense to have an expression such as delay().minutes.then(...). The count needs to be declared before the units, so the units object is kept in private storage and exposed by returning it from the for(count) call.

Creating Modifiers

With fluent APIs, it can be useful to declare modifiers that alter the behavior of all methods that descend from them in the object graph. For this, chainlang exposes the chainlang.proxy method. This allows you to create a copy of an object with all of its methods proxied. This is the same technique used by chainlang to create an object with chainable methods in chainlang.create.

var is = {};

// `is.even(...)` determines whether a value is even
is.even = function(){
    return (this._subject % 2 === 0);

// `isNot` has all the same methods of `is`, but negates their returns
var isNot = chainlang.proxy(is, function(fn){
    return function(){
        return !fn.apply(this, arguments);  

is.not = isNot;

is = chainlang.create(is);

// Logs: true

// Logs: false

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