typelib is a easy lowlevel, no-magic, no fuss, type definition library

The library helps you define struct-like structures, class-like structures, trait like structures and inheritable structures with simple merge functions, and javascript's native mechanisms. Unlike other libraries typelib encourages you to do it the javascript way! rather then trying to emulate structures from other languages.

npm install typelib

Using a package.json to manage dependencies?

• npm i -S typelib to install
• npm rm -S typelib to uninstall

USAGE

type.chain is a merge function that will create a new object with the prototype pointer set to the first paramter. Additional parameters passed to the function will be merged into the object. The function always returns a new object and accepts one or as many as you like paramters. Parameters are merged in order.

var type = require('typelib');
// ----------------------------------------------------------------------------

var MyOtherType = require('./MyOtherType');

var MyType = function (param1, param2, param3) {
	MyOtherType.call(this, param1, param2, param3);
};

MyType.prototype = type.chain(MyOtherType.prototype, SomeMixin, {

	// my stuff

});

module.exports = MyType;

type.merge is similar to type.chain but it only merges all the paramters into a single new object and doesn't do any prototype pointer manipulation; it's useful for extending mixins. Paramters are merged in order.

var type = require('typelib');
// ----------------------------------------------------------------------------

var Mixin1 = require('./Mixin1');
var Mixin2 = require('./Mixin2');

var MyMixin = type.merge(Mixin1, Mixin2, {

	// my stuff

});

module.exports = MyMixin;

type.props is a merge function that will ignore parameters that are null or undefined. Returns a new object that's the combination of the parameters merged in order.

var type = require('typelib');
// ----------------------------------------------------------------------------

var defaults = {
	// my props
};

var MyType = function (conf) {
	// no need to test conf, it's tested by type.props
	this._conf = type.props(defaults, conf);
};

module.exports = MyType;

On declaring types

There are a lot of libraries out there that offer a "inheritance mechanism." You don't need them! This very module is to some extent also one of those libraries and yes you don't necesarily need this module either!

I feel compelled to show you how you can do with out it entirely.

Do you just need a simple class-like structure?

Here you go,

var ExampleClass = function (name) {
	// this is your constructor
    this._name = name;
};

ExampleClass.prototype = {

	_greeting: 'hello',

    hello: function () {
    	console.log(this._greeting + ', ' + this.name);
    },

    name: function () {
    	return this._name;
    }

};

Now we can do this:

var example = new ExampleClass('world');
example.hello(); // => "hello, world"

If you need a equivalent of struct in javascript the above is almost always all you need.

How does that even work?

Let me break down the new ExampleClass('world') there into fundamental operations.

Here is what javascript does for you when you call a function using new:

// create a [new] object and set it's internal prototype mechanism pointer
// to point to the object defined in the property "prototype" of the
// function "ExampleClass"
var new_object = Object.create(ExampleClass.prototype);
// invoke the function setting [this] to [new object]
ExampleClass.call(new_object, 'world');

In the above, if you're not familiar with them,

• Object.create(object_to_use_as_prototype) creates a new empty object which has its internal prototype pointer set to the object passed as the first parameter
• .call invokes a function with the first parameter passed to the function as the variable this and all the other parameters passed in as regular function parameter

But I need to extend stuff!

Easy!

First, get a merge function that can combine the properties of two arbitrary number of objects, JQuery's $.extends, underscores or lodash's _.merge, node's require('util')._extend, whatever you can find will do! If you include Object.assign polyfill you can just use that instead. We'll assume you have it as an assign function in the example.

Now you just do,

var OtherType = require('./OtherType');
var SomeMixin = require('./SomeMixin');

var Example = function (param1, param2) {
	OtherType.call(this, param1, param2);
};

Example.prototype = assign(Object.create(OtherType.prototype), SomeMixin, {

	// your stuff

});

module.exports = Example;

So why use typelib?

typelib is really small, much smaller then libraries like underscore, lodash, jQuery, and so on.

The merge functions it provides are also specialized towards declaring types. The code from using them is also easier to understand for anyone that doesn't know the finer details of javascript, and easy for them to use to get going.

But hey if you can manage with out it, more power to you!