overwrite

Forget monkey-patching your dependencies. Completely rewrite any file in a third-party package/module on-the-fly!

Works with NPM v3+; untested on earlier versions.

Installation

Install the package with NPM:

$ npm install overwrite

Usage

As an example, consider the following code:

import isInteger from "is-integer";

console.log(isInteger(1)); // => true
console.log(isInteger(2)); // => true

If you wanted to modify/tweak the functionality of the third-party is-integer module (for some reason), you'd normally have three options:

1. Attempt to programmatically monkey-patch the module.
2. Fork the module, submit a patch to the original repository, and pray that it is merged.
3. Fork the module and publish your changes as a separate NPM package.

This package introduces a powerful fourth option – overwrite specific files in the module on-the-fly at runtime! For example:

import overwrite from "overwrite";

const isInteger = overwrite("is-integer", {
  "index.js": `
    module.exports = function(value) {
      return value === 1;
    }
  `
});

console.log(isInteger(1)); // => true
console.log(isInteger(2)); // => false

As can be seen, this package exposes a function that accepts a module name (string) as the first argument, and a mapping (object literal) of relative file paths to file contents as the second. The return value is the module itself (as if you called require or import), but with all of the overwrites applied. In this particular example, the index.js file in the third-party is-integer package is completely overwritten with new code that behaves very differently.

Tip

Most of the time, you probably won't want to completely overwrite the contents of a file, you'll just want to change a few lines here and there. You can easily do this by simply mapping the relative file path to a transformation function (instead of a string). Here's an example:

import overwrite from "overwrite";

const isInteger = overwrite("is-integer", {
  "index.js": contents => {
    let lines = contents.split("\n");
    lines.splice(3, 1, `console.log("Hello!");`);
    return lines.join("\n");
  }
});