babel-plugin-overload

This is an experimental plugin that allows you to overload operators in your Javascript code.

Compare with Python:

class Addable:
  def __add__(self, other):
    return # some computation which uses self and other

Using this Babel plugin:

class Addable {
  [Symbol.for('+')] (other) {
    return // some computation which uses this and other
  }
}

This plugin is still in beta and should be considered highly experimental. It should go without saying that you probably should not use this in production.

Example

In

x + y

Out

function (_left, _right) {
  if (_left !== null && _left !== undefined && _left[Symbol.for("+")]) return _left[Symbol.for("+")](_right);else return _left + _right;
}(x, y);

Supported Operators

At the moment, all binary operators are supported. Unary operators are coming soon.

The full supported list is:

• The arithmetic operators: +, -, /, *, %, **
• The bitwise operators: &, |, ^
• The bitshift operators: >>, <<, >>>, <<<
• The equality operators: ==, ===, !=, !==
• The inequality operators: >, <, >=, <=
• The remaining miscellaneous operators: in and instanceof

To overload any of them, define a method named with the Symbol you get with Symbol.for for the appropriate operator. For instance, use Symbol.for('+') to overload the + operator, and Symbol.for('in') to overload the in operator.

You can define the overloading method on the object itself or anywhere on the object's prototype chain.

At the moment, overloading is only supported for the left side value. Support for overloading on the right side value (the equivalent of Python's __radd__ family of methods) is coming soon.

Installation

$ npm install babel-plugin-overload

Usage

Via .babelrc (Recommended)

.babelrc

{
  "plugins": ["overload"]
}

Via CLI

$ babel --plugins overload script.js

Via Node API

require("babel-core").transform("code", {
  plugins: ["overload"]
});