require-array-sort-compare

Require Array#sort calls to always provide a compareFunction.

💭

This rule requires type information to run.

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 [ECMA specification].

The result is that elements are sorted alphabetically, regardless of their type. For example, when sorting numbers, this results in a "10 before 2" order:

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

This rule reports on any call to the Array#sort() method that doesn't provide a compare argument.

.eslintrc.cjs

module.exports = {
  "rules": {
    "@typescript-eslint/require-array-sort-compare": "error"
  }
};

Try this rule in the playground ↗

Examples

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

❌ 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

This rule accepts an options object with the following properties:

interface Options {
  /**
   * Whether to ignore arrays in which all elements are strings.
   */
  ignoreStringArrays?: boolean;
}

const defaultOptions: Options = [{ 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, and/or only ever sort arrays in a string-like manner, you can turn this rule off safely.

Resources

• Rule source
• Test source