Babel Macros

This is a Babel plugin adds support for hygienic, non-syntactic macros for JavaScript.

What?

Turns code like this:

DEFINE_MACRO(MAP, (input, visitor) => {
  const length = input.length;
  const result = new Array(length);
  for (let i = 0; i < length; i++) {
    result[i] = visitor(input[i], i, input);
  }
  return result;
});

function demo () {
  return MAP([1,2,3,4], item => item + 1);
}

Into code like this:

function demo() {
  var _input = [1, 2, 3, 4];

  var _visitor = function _visitor(item) {
    return item + 1;
  };

  var _map = undefined;

  var _length = _input.length;
  var _result = new Array(_length);
  for (var _i2 = 0; _i2 < _length; _i2++) {
    _result[_i2] = _visitor(_input[_i2], _i2, _input);
  }
  _map = _result;

  return _map;
}

Macro calls can also be chained, so if you declare a new macro called, e.g. FILTER:

DEFINE_MACRO(FILTER, (input, visitor) => {
  const filtered = [];
  for (let i = 0; i < input.length; i++) {
    if (visitor(input[i], i, input)) {
      filtered.push(input[i]);
    }
  }
  return filtered;
});

You'll then be able to combine the two macros in one statement, without needing to nest:

MAP([1, 2, 3], item => item + 1).FILTER(item => item < 4).length; // 2

Why?

Because macros are incredibly useful! Also because they make it easy to write extremely fast code without sacrificing readability. When compiled with closure elimination the above code is 10x faster than native Array.prototype.map().

Note: This is super experimental, use at your own risk!

Todo List

• Allow macros in macro definitions (currently causes infinite loop)
• Refactor for readability
• Allow macros to be imported and exported across files.
• Add DEFINE_TRANSFORM which is similar to DEFINE_MACRO but allows direct AST manipulation, not merely replacement.
• Implement function inlining for macro arguments (in the map example above, the _visitor function body should be inlined, removing the function entirely).

Installation

First, install via npm.

npm install --save-dev babel-plugin-macros

Then, in your babel configuration (usually in your .babelrc file), add "macros" to your list of plugins:

{
  "plugins": ["macros"]
}

License

Published by codemix under a permissive MIT License, see LICENSE.md.