close
Rslint

    prefer-then-catch

    Unreleased

    Configuration

    rslint.config.ts
    import { defineConfig, unicornPlugin } from '@rslint/core';

export default defineConfig([
  unicornPlugin.configs.recommended,
  {
    rules: {
      'unicorn/prefer-then-catch': 'error',
    },
  },
]);

    Rule Details

    Prefer .then(...).catch(...) over passing a rejection handler to .then(). A .catch handler attached after .then is reached both for rejections forwarded by .then and for rejections thrown from the fulfillment handler, while a second argument to .then is only called when the upstream promise itself rejects.

    The rule reports .then(fulfilled, rejected) calls when both handlers are non-nullish and the receiver type's .catch is callable. It offers a suggestion that rewrites the call to .then(fulfilled).catch(rejected) when the rejection handler can safely be moved (identifiers and function expressions qualify; calls with possible side effects do not).

    Examples of incorrect code for this rule:

    promise.then(onFulfilled, onRejected);

    Examples of correct code for this rule:

    promise.then(onFulfilled).catch(onRejected);

    When the rejection handler is a call with potential side effects, no suggestion is offered but the diagnostic still fires:

    promise.then(onFulfilled, createRejectionHandler());
// Diagnostic still fires; user must rewrite manually.

    Original Documentation