#prefer-single-call

#Configuration

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

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

Combine adjacent calls to Array#push(), Array#unshift(), Element#classList.add(), Element#classList.remove(), or importScripts().

This rule is enabled at error severity in unicornPlugin.configs.recommended.

#Rule Details

These methods accept multiple arguments. Calls must be adjacent expression statements on the same receiver. For unshift(), the second call's arguments come first so the resulting element order stays the same.

Examples of incorrect code:

const values = [];
values.push(1);
values.push(2, 3);

values.unshift(1);
values.unshift(2, 3);

element.classList.add('active');
element.classList.add('visible');

importScripts('first.js');
importScripts('second.js');

Examples of correct code:

const values = [];
values.push(1, 2, 3);
values.unshift(2, 3, 1);
element.classList.add('active', 'visible');
importScripts('first.js', 'second.js');

Known non-array receivers are ignored. Unknown array receivers receive a suggestion; known arrays are automatically fixed only when every argument has a static value without side effects. Arguments such as values.length and direct spreads such as values.push(...items) require a suggestion because merging changes when arguments run relative to the first mutation. For class lists and importScripts(), a side effect in the second call's arguments also requires a suggestion.

Comments in the text that would be removed suppress both fixes and suggestions. The rule preserves optional-chain behavior and does not replace loops with spread calls.

TypeScript's inferred receiver types also identify arrays. With static, side-effect-free arguments, these calls are automatically fixed:

const values = [0].map(value => value);
values.push(1);
values.push(2);

Static spreads inside array and object arguments are supported too. For example, values.push([...[1]]); values.push(2); is automatically merged into values.push([...[1]], 2);.

#Options

#ignore

An array of exact function or method paths to ignore. The default is [].

{
  "unicorn/prefer-single-call": [
    "error",
    { "ignore": ["readable.push", "element.classList.add", "importScripts"] }
  ]
}

Both push and unshift on stream, this, this.stream, process.stdin, process.stdout, and process.stderr are always ignored.

#Differences from upstream

rslint offers a suggestion instead of an automatic fix when a spread source is modified through a local alias or an operation such as Object.defineProperty(). This includes aliases created by destructuring and references copied into containers by Object.assign(). Visible changes to Array.prototype or String.prototype also make affected array or string spreads require a suggestion. For example, this custom iterator changes values while the second argument is evaluated:

const values = [];
const source = [1];
const alias = source;
alias[Symbol.iterator] = function* () {
  values.push(0);
  yield 1;
};
values.push(1);
values.push([...source]);

Automatically merging these calls would move the iterator's push(0) before push(1) and change the result. Review the suggestion before applying it.

Arguments that apply decorators or call custom template tags also require a suggestion, because those operations can run user code while evaluating the arguments.

#Original Documentation

• eslint-plugin-unicorn: prefer-single-call
• Source code