eslint/eqeqeq Pedantic

⚠️🛠️️ A dangerous auto-fix is available for this rule for some violations.

What it does

Requires the use of the === and !== operators, disallowing the use of == and !=.

Why is this bad?

Using non-strict equality operators leads to unexpected behavior due to type coercion, which can cause hard-to-find bugs.

Options

First option:

• Type: string
• Default: "always"

Possible values:

• "always" - always require ===/!==
• "smart" - allow safe comparisons (typeof, literals, nullish)

Second option (only used with "always"):

• Type: object
• Properties:
  • null: string (default: "always") - "ignore" allows == null and != null.

Possible values for null:

• "always" - always require === null/!== null
• "never" - always require == null/!= null
• "ignore" - allow both == null/!= null and === null/!== null

Example JSON configuration:

{
  "eqeqeq": ["error", "always", { "null": "ignore" }]
}

Examples

"always" (default)

Examples of incorrect code for this rule:

/* eslint eqeqeq: "error" */

if (x == 42) {}
if ("" == text) {}
if (obj.getStuff() != undefined) {}

Examples of correct code for this rule:

/* eslint eqeqeq: "error" */

if (x === 42) {}
if ("" === text) {}
if (obj.getStuff() !== undefined) {}

"smart"

Examples of incorrect code for this rule with the "smart" option:

/* eslint eqeqeq: ["error", "smart"] */

if (x == 42) {}
if ("" == text) {}

Examples of correct code for this rule with the "smart" option:

/* eslint eqeqeq: ["error", "smart"] */

if (typeof foo == "undefined") {}
if (foo == null) {}
if (foo != null) {}

{"null": "ignore"} (with "always" first option)

Examples of incorrect code for this rule with the { "null": "ignore" } option:

/* eslint eqeqeq: ["error", "always", { "null": "ignore" }] */
if (x == 42) {}
if ("" == text) {}

Examples of correct code for this rule with the { "null": "ignore" } option:

/* eslint eqeqeq: ["error", "always", { "null": "ignore" }] */
if (foo == null) {}
if (foo != null) {}

{"null": "always"} (default - with "always" first option)

Examples of incorrect code for this rule with the { "null": "always" } option:

/* eslint eqeqeq: ["error", "always", { "null": "always" }] */

if (foo == null) {}
if (foo != null) {}

Examples of correct code for this rule with the { "null": "always" } option:

/* eslint eqeqeq: ["error", "always", { "null": "always" }] */

if (foo === null) {}
if (foo !== null) {}

{"null": "never"} (with "always" first option)

Examples of incorrect code for this rule with the { "null": "never" } option:

/* eslint eqeqeq: ["error", "always", { "null": "never" }] */

if (x == 42) {}
if ("" == text) {}
if (foo === null) {}
if (foo !== null) {}

Examples of correct code for this rule with the { "null": "never" } option:

/* eslint eqeqeq: ["error", "always", { "null": "never" }] */

if (x === 42) {}
if ("" === text) {}
if (foo == null) {}
if (foo != null) {}

Configuration

This rule accepts a configuration object with the following properties:

compareType

type: "always" | "smart"

nullType

type: "always" | "never" | "ignore"

How to use

To enable this rule in the CLI or using the config file, you can use:

CLI

oxlint --deny eqeqeq

Config (.oxlintrc.json)

{
  "rules": {
    "eqeqeq": "error"
  }
}

References

• Rule Source