LouisBrunner/babel-plugin-transform-nullish-operator

A Babel plugin which emulates the `a?` existence check from CoffeeScript using the `??` syntax

babel-plugin-transform-nullish-operator

This package is a babel plugin which can be used to emulate the Coffeescript existence operator (a?) in Babel using the new coalescing nullish operator (Stage 4 proposal).

This is completely non-standard, experimental and could break at any time.

Example

In

var fooExists = object.foo ?? EXISTS;

Out

var _object$foo;

var fooExists = (_object$foo = object.foo) !== null && _object$foo !== void 0;

NOTE: We cannot use != null here because document.all == null and document.all has been deemed not "nullish".

Installation

npm install --save-dev babel-plugin-transform-nullish-operator

Usage

With a configuration file (Recommended)

{
  "plugins": ["babel-plugin-transform-nullish-operator"]
}

Via CLI

babel --plugins babel-plugin-transform-nullish-operator script.js

Via Node API

require("@babel/core").transform("code", {
  plugins: ["babel-plugin-transform-nullish-operator"]
});

Options

identifier

string, defaults to EXISTS.

Can be used to change the identifier which is used to trigger this alternative behavior of the nullish coalescing operator.

Example with {"identifier": "DO_YOU_EXIST"}

In

var fooExists = object.foo ?? DO_YOU_EXIST;

Out

var _object$foo;

var fooExists = (_object$foo = object.foo) !== null && _object$foo !== void 0;

Linting

Your linter might EXISTS as undefined (which is true, the symbol doesn't actually exists, it is only a placeholder), in that case you will need to explicitely add it in your config.

Example using eslint:

{
  ...
  "globals": {
    "EXISTS": "readonly"
  },
  ...
}

References & Thanks

This is project is heavily based on Babel's @babel/plugin-proposal-nullish-coalescing-operator (including code, tests, usage, etc).

License

MIT, Copyright (c) 2020-2020 Louis Brunner