Rule proposal: `no-top-level-side-effects`

Description

Opinionated, difficult/impossible to implement, and likely super annoying in practice.

Reasoning: importing a file should not have side effects

Related rules:

• https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/no-unassigned-import.md
• https://eslint.org/docs/rules/no-new

Fail

document.title = 'gone'

Pass

export function init () {
  document.title = 'gone'
}

function init () {
  document.title = 'gone'
}

// Optional? Still a side effect, but at least it's wrapped
// and not lost between many function declarations.
// Maybe a single, unassigned function call per file could be allowed
init(); 

// Optional? Assignments could be considered side-effect free for the sake of usability
const details = new Map();
const response = fetch(); // even if they're not, really
const memoizedFetch = mem(fetch);

// in ./polyfill.js

// Optional? Some exceptions could be made by filename 
document.title = 'gone'

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Backers (Total: $20.00)

• fregante ($20.00)

Submitted pull Requests

• #2957 Add no-top-level-side-effects rule

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