Enforce the use of u flag on RegExp

๐Ÿ’ก hasSuggestions

Some problems reported by this rule are manually fixable by editor suggestions

RegExp u flag has two effects:

  1. Make the regular expression handling UTF-16 surrogate pairs correctly.

    Especially, character range syntax gets the correct behavior.

    /^[๐Ÿ‘]$/.test("๐Ÿ‘") //โ†’ false
    /^[๐Ÿ‘]$/u.test("๐Ÿ‘") //โ†’ true
  2. Make the regular expression throwing syntax errors early as disabling Annex B extensions.

    Because of historical reason, JavaScript regular expressions are tolerant of syntax errors. For example, /\w{1, 2/ is a syntax error, but JavaScript doesnโ€™t throw the error. It matches strings such as "a{1, 2" instead. Such a recovering logic is defined in Annex B.

    The u flag disables the recovering logic Annex B defined. As a result, you can find errors early. This is similar to the strict mode.

Therefore, the u flag lets us work better with regular expressions.

Rule Details

This rule aims to enforce the use of u flag on regular expressions.

Examples of incorrect code for this rule:

/*eslint require-unicode-regexp: error */

const a = /aaa/
const b = /bbb/gi
const c = new RegExp("ccc")
const d = new RegExp("ddd", "gi")

Examples of correct code for this rule:

/*eslint require-unicode-regexp: error */

const a = /aaa/u
const b = /bbb/giu
const c = new RegExp("ccc", "u")
const d = new RegExp("ddd", "giu")

// This rule ignores RegExp calls if the flags could not be evaluated to a static value.
function f(flags) {
    return new RegExp("eee", flags)

When Not To Use It

If you donโ€™t want to notify regular expressions with no u flag, then itโ€™s safe to disable this rule.


This rule was introduced in ESLint v5.3.0.