babel-preset-more-optimization

Babel preset for additional optimization/minification.

If you stumble across this: NOT FOR PRODUCTION USE

Installation

npm install --save-dev babel-preset-more-optimization

Usage

.babelrc:

{
  "presets": [
    "more-optimization"
  ]
}

Or, with the unsafe option:

{
  "presets": [
    ["more-optimization", { "unsafe": true }]
  ]
}

...its behaviour is described in the following sections.

Optimizations

Flatten trivial IIFEs

In:

(() => {
	foo();
	bar.baz();
})();

var x = (function() {
	return 'x';
})();

(function() {
	var someBinding;
	if (or_someNontrivialControlFlow) bailout();
})();

Out:

foo();
bar.baz();

var x = 'x';

(function() {
	var someBinding;
	if (or_someNontrivialControlFlow) bailout();
})();

Eliminate calls of identity functions

In:

function id(x) { return x; }

var foo = id(baz(), 1, '2');

var bar = id(baz(), someOtherImpureArgument());

Out:

function id(x) { return x; }

var foo = baz();

var bar = id(baz(), someOtherImpureArgument());

unsafe option

With unsafe, calls of identity functions whose arguments are impure due to unreferenced identifiers are eliminated. This is unlikely to be unsafe in practice, as you'd have to be relying on side-effects of a global getter or a thrown ReferenceError.

In:

function toClass(val, class_) { return val; }

var x = toClass(a, HTMLAnchorElement);

Out:

function toClass(val, class_) { return val; }

var x = a;

Eliminate calls of Object.freeze and friends

This is intended primarily to facilitate SROA (below).

In:

var x = Object.freeze({ a: 5 });

Out:

var x = { a: 5 };

Scalar replacement of aggregates

In:

var x = {
	a: { b: 5 },
	c() {}
};

Out:

var _x$a$b = 5,
	_x$c = function c() {};

unsafe option

With unsafe, scalar replacement will be performed on objects whose properties are written to. This is unlikely to be unsafe in practice, as the assigned property (alone) would have to reference this. (This optimization always bails out if existing object properties reference this.)

In:

var x = {
	a: { b: 5 },
	c() {}
};

x.a.b *= 2;

Out:

var _x$a$b = 5,
	_x$c = function c() {};

_x$a$b *= 2;

Store-to-load forwarding / copy propagation

In:

var a = () => {};
var _a = a;
function foo() {
	var b = _a;
	function bar() {
		var c = b;
		c();
	}
}

Out:

var a = () => {};
function foo() {
	function bar() {
		a();
	}
}