InterPatcher 🐒

A library for patching, replacing and decorating javascript methods during runtime.

Also called monkey patching 🐒🐒🐒.

Source Code

The source code is available in GitHub.

Installation

npm i interpatcher

My first patch

// This prefixes the patched method with another method of our selection
addPrefix(targetObject, 'targetMethod', (prefixData) => {
  console.log("hello from a prefix");
});

Prefixes

Prefixes are patches that run before the original method.

addPrefix(targetObject, 'targetMethod', (prefixData) => {/**/});

The callback receives a PrefixData variable which keeps track of:

context : any, // The context from where the original method was called.
args : any[], // The arguments which were used to call the original method.
originalMethod : Function, // The original method so you can call it without causing overflows.
runOriginal : boolean, // Whether the original method should be skipped.
returnValue : any, // The return value in case you skip to run the original method.

So this allows you to completelly replace any method if you wanted to!

addPrefix(Math, 'abs', (prefixData) => {
  prefixData.runOriginal = false;
  prefixData.returnValue = -prefixData.args[0];
});

Postfixes

Postfixes are like prefixes, but they run after the original method instead.

addPrefix(targetObject, 'targetMethod', (postfixData) => {/**/});

The callback receives a PostfixData variable which keeps track of:

context : any, // The context from where the original method was called.
args : any[], // The arguments which were used to call the original method.
originalMethod : Function, // The original method so you can call it without causing overflows.
returnValue : any, // The return value (which is the original method value by default and can be replaced).

Unpatching

For unpatching just save the returned id for your prefix or postfix:

const prefixId = addPrefix(...);
unpatchPrefix(targetObject, targetMethod, prefixId);
const postfixId = addPostfix(...);
unpatchPostfix(targetObject, targetMethod, postfixId);

You can also unpatch all prefixes, postfixes and overrides from a patched method:

unpatchAll(targetObject, 'targetMethod');

Multi Prefixes, Postfixes and Overrides

Yes, you can have multiple prefixes, postfixes and overrides for a single method, they will run in order of registration, meaning that the later you register a method, the later it will run.