virtual-prototype

About

The temptation of extending prototypes is always there, lurking in the shadows when writing javascript, but it is never a good idea. Its abuse has prevented the development of the web (it's the reason why Array.prototype.contains won't exist any time soon).

I present to you a much safer solution. A wrapper that enables you to define methods on top of any type (except null and undefined), so that you can keep things nice and object oriented!

Usage

My recommended way to use this module is to create a extensions module for your project that exports an instance of VirtualPrototype. Then you can import that module throughout your project.

Another way to use the module would be to create an npm package containing a frozen singleton instance of set of utility (akin to lodash). After all methods have been added you can call finalize on the instance to prevent editing. This would also prevent monkey patching, so whether to do that is up to you.

Virtually extending types

var VirtualPrototype = require('virtual-prototype')
var vp = VirtualPrototype();
 
// define the types you wish to "extend"..
 
vp.defineType('string');       // checks type with typeof
vp.defineType('array', Array); // checks type with instanceof
 
// ..define the methods on the virtual prototypes.
 
vp.string.define('secondCharacter', function () {
    if (this.length < 2)
        return '';
    return this.charAt(1);
});
 
vp.array.define('last', function () {
    if (! this.length) {
        return null;
    }
 
    return this[this.length - 1];
});
 
vp('hello').secondCharacter(); // 'e'
 
vp([1, 2, 3]).last();          // 3

Creating methods for all types

var VirtualPrototype = require('virtual-prototype');
var vp = VirtualPrototype();
 
vp.appendString = function (str) {
    return this + str;
};
 
vp(9).appendString(' times');       // '9 times'
vp('Hello').appendString(' world'); // 'Hello world'

API documentation

vp.defineType

Arguments

typeAndIdentifier

Itentifier, constructor

Example

// Type checks using typeof (+ instanceof String if identifier is 'string')
vp.defineType('string');
 
// Type checks using instanceof
vp.defineType('array', Array);

vp.define

Arguments:

name, handler

Example

vp.define('toUppercaseString', function () {
    return this.toString().toUpperCase();
})
 
vp({}).toUppercaseString(); // '[OBJECT OBJECT]'

vp.<type>.define

Define a method on the virtual prototype for the given type. <type> must be defined using defineType and must match the first parameter given to defineType.

Example

 
// Using just type (matched with typeof)
vp.defineType('string');
 
vp.string.define('reverse', function () {
    var result = '';
 
    for (var i = this.length - 1; i >= 0; i--) {
        result += this[i];
    }
 
    return result;
});
 
// Using constructor function as second argument (matched with instanceof)
vp.defineType('array', Array);
 
vp.array.define('reverse', function () {
    for (var i = 0, j = this.length - 1; i < this.length/2; i++, j--) {
        var tmp = this[i];
        this[i] = this[j];
        this[j] = tmp;
    }
    return this;
});

vp.finalize

Prevent further changes to the instance of VirtualPrototype. After this, no new methods can be registered and no methods can be altered/deleted.

Testing

Node

npm test

Browser

• npm install --global browserify
• npm run browserify
• open browsers-test.html (and copy the url to the browser you wish to test in)

Tested in

• Node v4.2.0
• Chrome 50.0.2661.102
• Safari 9.1.1
• Firefox 46.0.1
• IE11

Notes

• Overriding functions using define(<existing-name>, <handler>) for a given type is illegal and will throw a TypeError.
• null/undefined can not be captured by vp() as they can not be referenced by this. Throws a TypeError.