Convert ES6 rest params to ES3:

var join = function(joinStr, ...items) {
  return items.join(joinStr);
};

becomes:

var join = function(joinStr) {
  var items = [].slice.call(arguments, 1);
  return items.join(joinStr);
};

Usage

var compile = require('es6-rest-params').compile;

var output = compile(mySource);  // outputs { code: "..." }

// or, for source maps:
var output = compile(mySource, {
  sourceFileName: 'foo.js',
  sourceMapName: 'foo.js.map'
});  // outputs { code: "...", map: {...} }

Resources

Source map example

Thanks to Facebook's jstransform for the implementation strategy :)