Why is this an issue?

Many of JavaScript’s Array methods return an altered version of the array while leaving the source array intact. reverse and sort do not fall into this category. Instead, they alter the source array in addition to returning the altered version, which is likely not what was intended.

This rule raises an issue when the return values of these methods are assigned, which could lead maintainers to overlook the fact that the original value is altered.

Noncompliant code example

const reversed = a.reverse(); // Noncompliant
const sorted = b.sort(); // Noncompliant

Compliant solution

const reversed = [...a].reverse();  // spread the contents of 'a' into a new array, so reverse doesn't impact 'a'
const reversed2 = a.toReversed(); // ES2023 method that copies and reverses the array
a.reverse(); // reverse the array in place

const sorted = [...b].sort(); // spread the contents of 'b' into a new array, so sort doesn't impact 'b'
const sorted2 = b.toSorted(); // ES2023 method that copies and sorts the array
b.sort(); // sort the array in place