ProtoXT - A new way to extend Object prototypes

A small library to allow you to safely add 'dynamic properties' to (the prototype of) objects, with the help of Symbols.

This may be useful for 'monkey patching' native JavaScript types to give them new capabilities.

Note: this library initially was a fork from the metho project (Jon Randy).

How to use

The script can be imported from https://kooiinc.github.io/ProtoXT/protoxt.js

ProtoXT is fairly simple. It offers either one function (default) or two basic functions. The default or first function (add) adds 'dynamic properties' to target object(s) (as a symbol). The non default addMethod createts an object with an enclosed function and properties that can later be added to Objects using a To-method.

The add/default function will return a Symbol.

The addMethod function returns an Object containing the To method to add an enclosed function to one or more Objects (prototypes) later. The To method returns a Symbol too.

The resulting Symbols are the property 'names'.

Using the default

Import the library:

import addMethod from [location of protox.js].

Now addMethod is available addMethod(targetOrTargets, function, [{outerSyntax: [true/false], symbolName: [a name]}])

When the default is used (let's call it addMethod) it is the only function you'll need.

It will use addWithParams or addSimple based on the arity (the number of parameters) of the passed function. An arity of 0 will cause addSimple to be used *). Anything else will cause addWithParams (outerSyntax: false) or addProperty (outerSyntax: true) to be used.

Using addExtensionFn

Import the library:

import {add, addExtensionFn: addMethod} from [location of protox.js].

Now the methods add and addMethod are available. The add-method is the same as the default.

addMethod(function, [{outerSyntax: [true/false], symbolName: [a name]}])

This delivers an Object with one method: To which enables you to add the enclosed function as (symbolic) extension to one ore more Objects (prototypes). For example:

  const logger = addMethod(function() { console.log(this, this.contructor); })
  // [... code cntd]
  const logCtor = logger.To(Array, RegExp, String);
  /[a-z]/g[logCtor] // => /[a-z]/g, f RegeXp() [...]
  `hello`[logCtor]  // => `hello`, f String() [...]

When added with option outerSyntax set to true the syntax for your property will be that of a more regular function call:

// options.outerSyntax = true
object[property](x)

Otherwise you use

// options.outerSyntax = false
object[property(x)]

There is a slight performance hit when not using outerSyntax - hence the reason for the switch. To specify more than one target for the function, you should pass an array of targets.

Some examples:

  import addMethod from 'protoxt';
  
  // number to hexadecimal
  const asHex = addMethod(
    Number,
    function () {
      return this.toString(16);
    }
  );
  console.log(65534[asHex]);  // fffe
  
  // string to uppercase
  const upper = addMethod(
    String,
    function () {
      return this.toUpperCase();
    }
  );
  
  // Note the default [length] value here
  const chunk = addMethod(
    String,
    function (length = 2) {
      return this.match(new RegExp('.{1,' + length + '}', 'g'))
    }
  );
  
  console.log("Hello World!"[upper][chunk(2)]);  // ['HE', 'LL', 'O ', 'WO', 'RL', 'D!']
  
  const dateFormatter = () => {
    const dateOnlyOptions = { 
      year: 'numeric', 
      month: 'long', 
      day: 'numeric', 
      timeZone: 'Europe/Amsterdam', };
    return addMethod(Date, function() { 
      return new Intl.DateTimeFormat(`nl-NL`, dateOnlyOptions).format(this); 
    });
  };
  
  const format = dateFormatter();
  
  console.log(new Date(`2029/03/02`)[format]); // 2 maart 2029

See also

*) With default parameter values or spreaded arguments the arity of a function may be 0. So this fork checks length, and uses a (ProtoXT Function extension) length method (hasArgs) to check if any such parameters with default parameters exist.