Murphy.js

A functional interface for information hiding and inheritance.

Murphy's Law: If there are two or more ways to do something, and one of those ways can result in a catastrophe, then someone will do it.

JavaScript does not provide an effective mechanism for encapsulating data.

"Classes" (and, in ECMAScript 6, the class keyword) do not provide syntactic support for private or protected fields.

class Person {
    constructor(name) {
        this._name = name;
    }
    hello() {
        console.log('Hi, my name is "' + this._name + '".');
    }
}

function Person(name) {
    this._name = name;
}
Person.prototype.hello = function () {
    console.log('Hi, my name is "' + this._name + '".');
};

var joe = new Person('Joe');
console.log(joe._name); // "Joe"

It is a major shortcoming that _name is accessible from the outside, because there is no reason for it to be, and it would be unreliable for a programmer to depend on its accessibility.

To achieve privacy, one must use var.

function Person(options) {
    var name = options.name;
    this.hello = function () {
        console.log('Hi, my name is "' + name + '".');
    };
}

But the data cannot be shared by inheritors.

class Mayor extends Person {
    constructor() {
        this.hello = function () {
            // ReferenceError: name is not defined
            console.log('Good day, citizen! My name is "' + name + '".');
        };
    }
}

We want "protected" data that can be accessed by the lineage but is inaccessible to the outside world.

Meet Murphy:

var makeConstructor = murphy();
var makePerson = makeConstructor(null, function (self, options) {
    self.protected.name = options.name;
    self.public.hello = function () {
        console.log('Hi, my name is "' + self.protected.name + '".');
    };
});
var makeMayor = makeConstructor(makePerson, function (self, options) {
    self.public.hello = function () {
        console.log('Good day, citizen! My name is "' + self.protected.name + '".');
    };
});

var person = makePerson({
    name: 'Joe'
});
person.hello(); // Hi, my name is "Joe".
console.log(person.name); // undefined

var mayor = makeMayor({
    name: 'Bob'
});
mayor.hello(); // Good day, citizen! My name is "Bob".
console.log(mayor.name); // undefined

With Murphy, you don't need "prototypal" constructors, new, this, or even the class keyword or () => {} ("fat arrow" functions). All you need is makeConstructor and function.

With Murphy, you can build extensible interfaces that don't expose private data. Thanks to encapsulation, the things that can go wrong when _pinkyPromises are $$violated, cannot go wrong.

Installation

Browser:

bower install --save murphy

<script src="bower_components/murphy/murphy.js"></script>

Node:

npm install --save murphy

Usage

Via browser global:

var makeConstructor = murphy();

AMD:

require(['murphy'], function (murphy) {
    var makeConstructor = murphy();
});

CommonJS:

var murphy = require('murphy');
var makeConstructor = murphy();

Development

To run tests in Node.js:

npm test

To run tests in a browser, open test.html.

License

MIT.