Rollup, multiple files, same constants name in multiple files: error in browser: Uncaught SyntaxError: Identifier 'o' has already been declared

Question

I have a problem.

EXPLANATION

In a website I navigate on page /one, the code in the one.js file executes fine.

After a while I insert in the page (pjax, ajax: no matter how) the second code in two.js file.

The browser complains with this error:

Uncaught SyntaxError: Identifier 'o' has already been declared
- at two.js:1

REPRODUCTION and SOURCE CODE

1. rollup.config.js:

   import resolve from 'rollup-plugin-node-resolve'
   import commonjs from 'rollup-plugin-commonjs'
   import { terser } from 'rollup-plugin-terser'
   import multiInput from 'rollup-plugin-multi-input'
   
   export default {
     input: ['src/**/*.js'],
     output: {
       format: 'esm',
       dir: 'dist/js'
     },
     plugins: [
       multiInput({ relative: 'src' }),
       resolve({ browser: true }),
       commonjs(),
       terser()
     ]
   }
   

2. src/one.js:

   const names1 = ['john1', 'carl1', 'bob1']
   names1.forEach(name1 => {
     console.log('name1:', name1, ', in names1:', ...names1)
   })
   

3. src/two.js:

   const names2 = ['john2', 'carl2', 'bob2']
   names2.forEach(name2 => {
     console.log('name2:', name2, ', in names2:', ...names2)
   })
   

4. dist/js/one.js:

   const o=["john1","carl1","bob1"];o.forEach(n=>{console.log("name1:",n,", in names1:",...o)});
   

5. dist/js/two.js:

   const o=["john2","carl2","bob2"];o.forEach(n=>{console.log("name2:",n,", in names2:",...o)});
   

QUESTIONS

How to fix this problem?

Can we "prefix" constants name based on file name?

If of course I put everything in just one.js file it works but it's not possible because of the structure of the project.

Answer 1

You chose output.format: 'esm', which makes Rollup assume that the codes live in their own module scope. If you insert them in your page with

 <script type="module" src="/dist/js/one.js"></script>
 <script type="module" src="/dist/js/two.js"></script>

I would expect them to work. If you don't want to use type="module", then use a different output format for Rollup which will wrap them in a module pattern (or IIFE) to give them their own scopes.