Requires Array#sort calls to always provide a compareFunction (require-array-sort-compare)

This rule prevents invoking the Array#sort() method without providing a compare argument.

When called without a compare function, Array#sort() converts all non-undefined array elements into strings and then compares said strings based off their UTF-16 code units.

The result is that elements are sorted alphabetically, regardless of their type. When sorting numbers, this results in the classic "10 before 2" order:

[1, 2, 3, 10, 20, 30].sort(); //→ [1, 10, 2, 20, 3, 30]

This also means that Array#sort does not always sort consistently, as elements may have custom #toString implementations that are not deterministic; this trap is noted in the language specification thusly:

note

Method calls performed by the ToString abstract operations in steps 5 and 7 have the potential to cause SortCompare to not behave as a consistent comparison function.

https://www.ecma-international.org/ecma-262/9.0/#sec-sortcompare

Rule Details

This rule aims to ensure all calls of the native Array#sort method provide a compareFunction, while ignoring calls to user-defined sort methods.

Examples of code for this rule:

❌ Incorrect

const array: any[];
const stringArray: string[];

array.sort();

// String arrays should be sorted using `String#localeCompare`.
stringArray.sort();

✅ Correct

const array: any[];
const userDefinedType: { sort(): void };

array.sort((a, b) => a - b);
array.sort((a, b) => a.localeCompare(b));

userDefinedType.sort();

Options

The rule accepts an options object with the following properties:

type Options = {
  /**
   * If true, an array which all elements are string is ignored.
   */
  ignoreStringArrays?: boolean;
};

const defaults = {
  ignoreStringArrays: false,
};

ignoreStringArrays

Examples of code for this rule with { ignoreStringArrays: true }:

❌ Incorrect

const one = 1;
const two = 2;
const three = 3;
[one, two, three].sort();

✅ Correct

const one = '1';
const two = '2';
const three = '3';
[one, two, three].sort();

When Not To Use It

If you understand the language specification enough, you can turn this rule off safely.

Attributes

• ✅ Recommended
• 🔧 Fixable
• 💭 Requires type information