A babel-macro that makes for-in only visit own properties

The problem

for ... in statements get enumerable keys from the whole prototype chain. To prevent bugs, it is reccomented to write loops like this:

for (const key in obj) {
  if (obj.hasOwnProperty(key)) {
    // "key" is a property of "obj"
  }
}

Pretty verbose, right?

This solution

This is a babel-plugin-macro which allows you to iterate only over own keys of an object when using for ... in.

Installation

This module can be installed either with npm or with yarn, and should be installed as one of your project's devDependencies:

npm install --save-dev for-own.macro

# or

yarn add --dev for-own.macro

Usage

Once you have configured babel-plugin-macros you can import/requie import-all.macro.

Here is an example:

import own from "for-own.macro";

for (const key in own(obj)) {
  const value = obj[key];
}

//     ↓ ↓ ↓ ↓ ↓ ↓

for (const key in obj) if (Object.hasOwnProperty.call(obj, key)) {
  const value = obj[key];
}

Caveats

The own macro only works inside for ... in loops. This code will throw an error at compile time:

const ownProps = own(obj);

LICENSE

MIT