patcharan

Patch and unpatch JavaScript functions multiple times, with the ability to remove patches in any order.

Install

npm install patcharan

Usage

import { patch, unpatch } from 'patcharan';

const mod = {
  greet(name) {
    return `hello ${name}`;
  },
};

// Define a patcher: receives the original and returns a wrapped version
const loud = (orig) => {
  return function (...args) {
    return orig.apply(this, args).toUpperCase();
  };
};

patch(mod, 'greet', loud);
mod.greet('world'); // => "HELLO WORLD"

unpatch(mod, 'greet', loud);
mod.greet('world'); // => "hello world"

Stacking patches

Multiple patches can be applied to the same function. Each patch wraps the result of the previous one. When a patch is removed with unpatch, the remaining patches are re-applied in order so the function stays consistent.

const logger = (orig) =>
  function (...args) {
    console.log('called with', args);
    return orig.apply(this, args);
  };

const timer = (orig) =>
  function (...args) {
    const start = performance.now();
    const result = orig.apply(this, args);
    console.log(`took ${performance.now() - start}ms`);
    return result;
  };

patch(mod, 'greet', logger);
patch(mod, 'greet', timer);

// Remove logger while keeping timer
unpatch(mod, 'greet', logger);

API

patch(obj, name, patcher)

Wraps obj[name] with the function returned by patcher.

• obj — the object that owns the function
• name — property name of the function to patch
• patcher (original) => replacement — receives the current function and must return the replacement

unpatch(obj, name, patcher)

Removes a previously applied patcher and rebuilds obj[name] from the remaining patches.

Arguments are the same as patch.

License

MIT