1.0.1 • Public • Published


Creates "chainable", proxied things.

This module isn't inherently useful by itself, but is a base for creating other useful things.

chainable uses Proxy objects to create "chainables". Chainables are simply a set of objects strung together using Proxy traps. For example:

import Chainable from '@jasonpollman/chainable';

const chainable = Chainable();
console.log(chainable.x.y.z); // Prints 'x.y.z'.

There's a number of practical uses for chainables:

  • Creating a fetch library where the user uses dot notation to specify a url endpoint
  • Creating a SQL generator (i.e. select('COL1', 'COL2').from('MY_TABLE').where(...))
  • [Insert imagination...]

The point, if you're wondering, is all about the resulting string evaluation of a chainable. The user will make some references a.b.c, etc. and it's up to the implementor to determine how to process the chainable's toString value.


$ npm install @jasonpollman/chainable --save

About Chainables


Each chainable object contains a set of tokens that represent its ancestry of "gets".

For example, in:

import Chainable from '@jasonpollman/chainable';

const chainable = Chainable();
const baz = chainable.foo.bar.baz;

baz's tokens are ['foo', 'bar', 'baz']. Note the initial reference to the chainable (chainable) isn't included in the tokens.


Each chainable has a .toString method that will join these tokens using the chainable's separator property.

console.log(baz.toString()); // Prints "foo.bar.baz"

By default a chainable's separator property is . (a period).

Storing References

Chainables can be sub-referenced since each time a property is accessed a new chainable object is created. For example:

import Chainable from '@jasonpollman/chainable';

const chainable = Chainable();

// Prints "foo.bar.baz"

const foo = chainable.foo;
const bar = chainable.bar;
// Prints "foo.bar.baz", but now I can also do...

// Prints "foo.bar.quxx".

Adding Value

When a user attempts to access a chainable's property, if it exists on the chainable object (or its prototype) the original value is returned. If the property doesn't exist a new chainable is returned (therefore creating the "chained dot notation" behavior).

This is useful, since we can extend our chainable with methods. For example, if I wanted to create an HTTP module using node-fetch I could do:

// Note this is a contrived example...

import fetch from 'node-fetch';
import Chainable from '@jasonpollman/chainable';

const api = Chainable({
  // Prefixed to the `toString` method
  prefix: 'http://my-api.com',
  // The "glue" that joins the tokens in the `toString` method
  separator: '/',
  // Implement all methods that each endpoint can call...
  get({ headers, query } = {}) {
    return fetch(...);
  post({ headers, body } = {}) {
    return fetch(...);

await api.foo.bar.baz.get();
// Makes a GET request to http://my-api.com/foo/bar/baz

await api.foo.bar.baz.post({ body: JSON.stringify({ ... }) });
// Makes a POST request to http://my-api.com/foo/bar/baz


chainable({Object} options) => {Proxy}

Default Export
Creates a chainable proxy object using the supplied options.

import Chainable from '@jasonpollman/chainable';

const chainable = Chainable({ /* options */ });


Property Type Default Description
prefix string|function|null null A string to prepend to the chainable's toString result.
suffix string|function|null null A string to append to the chainable's toString result.
sanitize function _.identity A function that provides an opportunity to sanitize the toString result when all links are joined.
sanitizeLinks function _.identity A function called on each token, providing the chance to sanitize it.
separator string|function . The "glue" to use when all of the chainable's tokens are joined.
invocableLinks boolean false If true chainable links will be functions, not objects and can invoked.
handleLinkInvocation function _.noop The function that's called when a chainable is invoked, only applies when invocableLinks is true

chainableGeneratorWithDefaults({Object} defaults) => {function}

Creates a new chainable generator with the supplied defaults. That is, a function that will combine the given defaults with the options provided to the returned function. This is intended for creating libraries. Using the example above (an api), we can export an api but not specify the "host" (prefix):

import { chainableGeneratorWithDefaults } from '@jasonpollman/chainable';

const APIBase = chainableGeneratorWithDefaults({
  separator: '/',
  get({ headers, query } = {}) {
    return fetch(...);
  post({ headers, body } = {}) {
    return fetch(...);

export default (host) => {
  return APIBase({ prefix: host });

Invocable Chainables

Chainable objects can be invocable (functions) too.
By default {} is the template used to create new chainable objects, however if you pass invocableLinks as true and supply a handleLinkInvocation function, you can control what happens when a chainable link is invoked.

import Chainable from '@jasonpollman/chainable';

const chainable = Chainable({
  invocableLinks: true,
  handleLinkInvocation: (link, value) => {
    console.log(`Property ${link.property} invoked with ${value}!`);

// Prints:
// "Property foo invoked with 1!"
// "Property bar invoked with 2!"
// "Property baz invoked with 3!"

The handleLinkInvocation is called with the chainable object as the first argument. All remaining arguments are passed as supplied to the link call.

There is a caveat to invocable chainables: They will always return another chainable. Therefore, the return value from your handleLinkInvocation method is ignored and cannot be awaited.

You can determine the property that was invoked using the link.property property.


This module requires native Proxy. A polyfill won't work!
Since properties must exist on an object in order for them to be intercepted, replicating this functionality using purely JavaScript is (AFAIK) impossible.


For now, chainables are limited to Node 6+ and will work in Chrome/Firefox. But hey, if you don't care about IE, go for it.

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npm i @jasonpollman/chainable

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