rollup-plugin-optimize-arguments

Rollup plugin to analyze for usage of arguments and automatically convert it to an array, to avoid leaking the arguments object (which is an optimization killer).

Basically, you can just use arguments as if it were a normal array and this plugin will take care of the rest.

Installation

npm install --save-dev rollup-plugin-optimize-arguments

Usage

var rollup = require('rollup').rollup;
var optimizeArguments = require('rollup-plugin-optimize-arguments');

rollup({
  entry: 'main.js',
  plugins: [
    optimizeArguments()
  ]
}).then(...)

Examples

Example input:

function foobar() {
  return arguments;
}

Output:

function foobar() {
  var $_len = arguments.length, $_args = new Array($_len); while ($_len--) { $_args[$_len] = arguments[$_len]; }
  return $_args;
}

Or even nested:

function foobar() {
  console.log(arguments);
  (function foobaz() {
    console.log(arguments);
    (() => {
      console.log(arguments);
      var toto = function () {
        console.log(arguments);
        !function() {
          console.log(arguments);
        }()
      }
      toto();
    })();
  })();
}

Output:

function foobar() {
  var $_len = arguments.length, $_args = new Array($_len); while ($_len--) { $_args[$_len] = arguments[$_len]; }
  console.log($_args);
  (function foobaz() {
    var $_len = arguments.length, $_args = new Array($_len); while ($_len--) { $_args[$_len] = arguments[$_len]; }
    console.log($_args);
    (() => {
      console.log($_args);
      var toto = function () {
        var $_len = arguments.length, $_args = new Array($_len); while ($_len--) { $_args[$_len] = arguments[$_len]; }
        console.log($_args);
        !function() {
          var $_len = arguments.length, $_args = new Array($_len); while ($_len--) { $_args[$_len] = arguments[$_len]; }
          console.log($_args);
        }();
      };
      toto();
    })();
  })();
}

(Arrow functions do not create their own scope and thus inherit their parent's arguments.)

This plugin also intelligently avoids creating unnecessary $_args objects in cases where usage is safe:

function foobar() {
  for (var i = 0; i < arguments.length; i++) {
    console.log(arguments[i]);
  }
}

Credits

Thanks to Rich Harris for rollup-plugin-inject and Alex Lur for rollup-plugin-ignore which I based this codebase off of.