transform commonjs: show warning on import/export of reserved keyword

[milahu]

this works in es5

exports.new = function() {};

this fails in es6

export function new() {}

cos new is a reserved keyword

only solution is to rename the export/import
lebab should at least show a warning

[frank-dspeed]

This is a nice One! i will write about that in my book thanks for supplying this but let me show you a importent code style change when you code esModules

exports.new = function() {}; // Wrong Really bad!

'use strict' // Only needed in the first file but is here for education
const new = function() {}; // This already errors even in es5
exports.new = new; // Good thing we assign to exports a already defined var

Welcome to Node.js v17.1.0.
Type ".help" for more information.
> const new = ''
const new = ''
      ^^^

Uncaught SyntaxError: Unexpected token 'new'
> 

this error is also already correctly catched by eslint and typescript so this can be closed its out of scope for lebab to run such checks before the main transform applys while i think it would be nice to add something that changes

exports.new = function() {};

to

const new = function() {}; 
exports.new = new;

and use that as pre transform so that people could check if that cjs code runs before they apply the import/export transform