1.0.19 • Published 9 years ago

proto v1.0.19

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9 years ago


A prototype-based inheritance/class library that makes it easy to create objects and inheritance hierarchies without losing the power of javascript's prototype system.

Why Use proto?

  • proto plays nice - you can use proto to inherit from any object, even if it was created with a different inheritance library!
  • instanceof works with proto classes
  • constructors are inheritable
  • non-objects can be returned from a constructor (even undefined)!
  • easy access to an object's superclass
  • you can give your classes dynamic names
  • you don't hafta use the new operator
  • native objects work with proto. proto properly creates classes that inherit from native objects - even all the Error types. Inheriting certain native javascript objects has some limitations (see below)
  • prototype and constructor properties are propertly set
  • proto doesn't use Object.create so it should work with older browsers ( testers welcome! )
  • proto is small: (833 bytes minified and gzipped in UMD format)
  • proto is lightweight. It doesn't attempt to emulate class-based languages or create any fancy features you probably don't actually need (interfaces, abstract classes, etc)
  • It has solid comparison when compared to the fastest inheritance libraries. The following two performance tests use specific methodology to improve their similarity to running code in the real applications:


var Person = proto(function() {       // prototype builder
    this.init = function(legs, arms) {      // constructor
        this.legs = legs
        this.arms = arms

    this.getCaughtInBearTrap = function() { // instance method
        this.legs -= 1
    this.limbs = function() {
        return this.arms + this.legs
    Object.defineProperty(this, 'limbs', { // getters (and setters, etc) can be set right on the prototype!
        get: function() {
            return this.arms + this.legs


var Girl = proto(Person, function() {       // inheritance
    this.haveBaby = function() {
        return Person(2,2)

var g = Girl(2,2)                          // instantiation
console.log("Girl has "+g.limbs+" limbs")
console.log(": (")

var newPerson = g.haveBaby()
console.log("New person has" +newPerson.limbs+" limbs : )")


npm install proto


Accessing proto:

// node.js
var proto = require('proto')

// amd
require.config({paths: {proto: '../generatedBuilds/proto.umd.js'}})
require(['proto'], function(proto) { /* your code */ })

// global variable
<script src="proto.umd.js"></script>
proto; // proto.umd.js can define proto globally if you really
       //   want to shun module-based design

Using proto:

var Parent = proto(function() {
    this; // points to the prototype, so set methods and static properties on this

    // the name property has an impact on how proto classes are displayed in dev tools
    this.name = 'MyProto'; // set a name for your proto class

    this.init = function(v) {   // constructor
        this; // inside methods, 'this' references the instance

        if(v > 0) {
            this.x = v                // you can normally access the object with this inside methods
        } else if(v !== undefined) {
			return true	              // you can return non-object values
		} else {
			return proto.undefined    // return undefined by using a special constructor return value

    this.anythingElse = 5   // static properties can be accessed by the class and the instance

    // getters and setters (enumerable makes it available statically too! Ie)
    Object.defineProperty(this, 'moose', {
        enumerable: true,
        get: function() {
            return 5
        set: function() {
            console.log("just kidding, i'm not setting anything!")

	// private functions don't have access to the correct 'this', so pass it in
    var privateFn = function(that, arg1, etc) {
        that.x = arg1 + etc

    this.doSomething = function() {
        privateFn(this, this.x, 1)

Parent.name;  // the name property can be accessed directly from the returned proto class object

// you can inherit from any object!
// the resulting object factory will generate instances inheriting from:
    // [if you inherit from]
        // [a function]: that function's prototype
        // [anything else]: that object itself
var Child = proto(Parent, function(superclass) {
    this.init = function() {
        superclass.init.apply(this, arguments) // super-class method call
        // superclass.prototype.someMethod.apply(this, arguments) // remember that you probably need to access superclass.prototype for parents that aren't proto objects
        // superclass.apply(this, arguments) // also remember that parents that aren't proto objects probably won't have an init method, but are constructors themselves (note that this should't be done with proto objectsbecause its creates a new instance)
        this.r = 10

	// create static methods just like instance methods - you can access them from the constructor
    this.staticMethod = function(x) {
        return this.constructor(x+12)        // uses its own constructor to create a Child object

var object = Child(1)                // instantiation
object.doSomething()                 // method call (as usual)
var object2 = Child.staticMethod(1)  // static method call

Child.parent === Parent; // the 'parent' property on the will point to the proto class's parent

Creating a custom Error object:

var CustomError = proto(Error, function(superclass) {
    this.name = 'CustomError'

    this.init = function(msg, properties) {
        superclass.call(this, msg)
        for(var n in properties) {
            this[n] = properties[n]

Limitations of proto

  • Inheriting from Error and other exception types doesn't automatically set a correct name property, so you need to set it as a static properly "manually".
  • Objects inheriting from String can't use the toString method.
  • Inheriting from Array doesn't work.
  • Inheriting from RegExp doesn't work either (the results can't use the test or match methods).
  • You can't properly access any non-writable properties of a function from the returned proto-object factory though the properties will work correctly on instances. This includes: name, length, arguments, and caller.
  • Some properties are read-only and so can't be reset on the prototype object. An example is name on firefox.


  • Browser testing
  • Chrome x
  • Firefox x
  • Safari x
  • IE11
  • IE10
  • IE9
  • IE8
  • Opera

  • performance improvements

    • Combine ProtoObjectFactory with the NamedFunction so you remove a function call there
    • memoize whether the class has 'init' or not (to remove one branch from ProtoObjectFactory)
  • Consider creating a Proto2 that focuses on further performance improvements:

    • Requires the use of 'new'
    • Maybe sacrifices dynamic prototypes (that change after constructor creation) to get rid of the prototype chain walking (and just merges in functions)

How to Contribute!

Anything helps:

  • Creating issues (aka tickets/bugs/etc). Please feel free to use issues to report bugs, request features, and discuss changes
  • Updating the documentation: ie this readme file. Be bold! Help create amazing documentation!
  • Submitting pull requests.

How to submit pull requests:

  1. Please create an issue and get my input before spending too much time creating a feature. Work with me to ensure your feature or addition is optimal and fits with the purpose of the project.
  2. Fork the repository
  3. clone your forked repo onto your machine and run npm install at its root
  4. If you're gonna work on multiple separate things, its best to create a separate branch for each of them
  5. edit!
  6. If it's a code change, please add to the unit tests (at test/protoTest.js) to verify that your change
  7. When you're done, run the unit tests and ensure they all pass
  8. Commit and push your changes
  9. Submit a pull request: https://help.github.com/articles/creating-a-pull-request


Change Log

  • 1.0.18 - Setting the 'stack' property of custom errors as 'configurable' so you can change it if you want
  • 1.0.17 - Correcting distribution
  • 1.0.16 - optimizing instance creation - made it about 3 times as fast! Now its one of the fastest inheritance libraries!
  • 1.0.15 - changing to using webpack to make UMD packages
  • 1.0.14 - fixing the name property so if there is no name, 'undefined' doesn't become the functions name
  • 1.0.13 - adding a 'parent' property on the returned proto class
  • 1.0.12 - making the constructor's name property settable (via this.name in the class construction function - the function passed to proto)
  • 1.0.11 - adding the ability to access getters and setters correctly statically
  • 1.0.10 - making the stack property a getter (like it is in native error objects)
  • 1.0.8 - if a static property can't be written (because it's read only or for some other reason throws an exception when being set), it will now silently not set, instead of throwing an exception
  • 1.0.7 - getting rid of useless line in stack trace
  • 1.0.6 - fixing custom error name in stacktraces
  • 1.0.5 - fixing github dependencies


Released under the MIT license: http://opensource.org/licenses/MIT