#no-return-array-push

#Configuration

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

export default defineConfig([
  unicornPlugin.configs.recommended,
  {
    rules: {
      'unicorn/no-return-array-push': 'error',
    },
  },
]);

#Rule details

Disallow using the return value of Array#push() or Array#unshift() when the call has at least one argument. Both methods return the updated array length. Read .length after the mutation when you need that value.

The rule allows standalone calls and calls whose results are discarded with void. It also allows member access on the result, as in router.push(to).catch(handleError), and skips receivers such as Map and Set when it can identify their type. Common router and stream push() calls are allowed unless the rule identifies the receiver as an array.

A direct return inside a block can offer an editor suggestion that moves the call before a bare return.

Examples of incorrect code for this rule

function add(item) {
  return items.push(item);
}

const length = items.unshift(item);
source.forEach(item => target.push(item));

Examples of correct code for this rule

function add(item) {
  items.push(item);
  return;
}

items.unshift(item);
const length = items.length;
target.push(...source);
void items.push(item);

#Options

This rule has no options.

#Differences from upstream

Rslint can identify a non-array receiver from an explicit JSDoc cast in JavaScript. In this example, Rslint allows the custom push() call. Unicorn v79.0.0 can report it when run without type information.

class Queue {
  push(value) {
    return value;
  }
}

const queue = /** @type {Queue} */ (readQueue());
const value = queue.push(1);

When ESLint is configured with TypeScript type information for JavaScript, Unicorn can infer that stream is an array in the example below. Rslint allows this call. Add /** @returns {number[]} */ to read for Rslint to identify the array and report the call.

function read() {
  return [];
}

const stream = read();
const length = stream.push(1);

#Original documentation

• Upstream documentation
• Upstream source