#promise/no-nesting

#Configuration

import { defineConfig, promisePlugin } from '@rslint/core';

export default defineConfig([
  promisePlugin.configs.recommended,
  {
    rules: {
      'promise/no-nesting': 'error',
    },
  },
]);

#Rule Details

Disallow nesting .then() or .catch() statements inside promise callbacks when the inner call does not depend on variables introduced by the enclosing callback.

Deeply nested promise chains are harder to read and can usually be rewritten as a flat chain. This rule flags the inner .then() / .catch() when its arguments do not reference any binding (parameter or local variable) that belongs to the immediately enclosing promise callback, because in that case the nesting is unnecessary.

Examples of incorrect code for this rule:

doThing().then(function () {
  return a.then();
});

doThing().then(() => b.catch());

doThing().then(function () {
  return a.then(function () {
    return b.catch();
  });
});

Examples of correct code for this rule:

// Flat chain — no nesting
doThing().then(function () {
  return 4;
});

// Inner call uses a closure variable from the enclosing callback — cannot be flattened
doThing().then((a) => getB(a).then((b) => getC(a, b)));

// Promise.resolve / Promise.all inside a callback is fine
doThing().then(function () {
  return Promise.resolve(4);
});

#Original Documentation

https://github.com/eslint-community/eslint-plugin-promise/blob/main/docs/rules/no-nesting.md