Rules

Rules are the core building block of ESLint. A rule validates if your code meets a certain expectation, and what to do if it does not meet that expectation. Rules can also contain additional configuration options specific to that rule.

ESLint comes with a large number of built-in rules and you can add more rules through plugins. You can modify which rules your project uses with either configuration comments or configuration files.

Rule Severities

To change a rule’s severity, set the rule ID equal to one of these values:

• "off" or 0 - turn the rule off
• "warn" or 1 - turn the rule on as a warning (doesn’t affect exit code)
• "error" or 2 - turn the rule on as an error (exit code is 1 when triggered)

Using configuration comments

To configure rules inside of a file using configuration comments, use a comment in the following format:

/* eslint eqeqeq: "off", curly: "error" */

In this example, eqeqeq is turned off and curly is turned on as an error. You can also use the numeric equivalent for the rule severity:

/* eslint eqeqeq: 0, curly: 2 */

This example is the same as the last example, only it uses the numeric codes instead of the string values. The eqeqeq rule is off and the curly rule is set to be an error.

If a rule has additional options, you can specify them using array literal syntax, such as:

/* eslint quotes: ["error", "double"], curly: 2 */

This comment specifies the “double” option for the quotes rule. The first item in the array is always the rule severity (number or string).

Configuration Comment Descriptions

Configuration comments can include descriptions to explain why the comment is necessary. The description must occur after the configuration and is separated from the configuration by two or more consecutive - characters. For example:

/* eslint eqeqeq: "off", curly: "error" -- Here's a description about why this configuration is necessary. */

/* eslint eqeqeq: "off", curly: "error"
    --------
    Here's a description about why this configuration is necessary. */

/* eslint eqeqeq: "off", curly: "error"
 * --------
 * This will not work due to the line above starting with a '*' character.
 */

Using configuration files

To configure rules inside of a configuration file, use the rules key along with an error level and any options you want to use. For example:

{
    "rules": {
        "eqeqeq": "off",
        "curly": "error",
        "quotes": ["error", "double"]
    }
}

And in YAML:

---
rules:
  eqeqeq: off
  curly: error
  quotes:
    - error
    - double

Rules from Plugins

To configure a rule that is defined within a plugin, prefix the rule ID with the plugin name and /.

In a configuration file, for example:

{
    "plugins": [
        "plugin1"
    ],
    "rules": {
        "eqeqeq": "off",
        "curly": "error",
        "quotes": ["error", "double"],
        "plugin1/rule1": "error"
    }
}

And in YAML:

---
plugins:
  - plugin1
rules:
  eqeqeq: 0
  curly: error
  quotes:
    - error
    - "double"
  plugin1/rule1: error

In these configuration files, the rule plugin1/rule1 comes from the plugin named plugin1, which is contained in an npm package named eslint-plugin-plugin1.

You can also use this format with configuration comments, such as:

/* eslint "plugin1/rule1": "error" */

Note: When specifying rules from plugins, make sure to omit eslint-plugin-. ESLint uses only the unprefixed name internally to locate rules.

Disabling Rules

Using configuration comments

To disable rule warnings in a part of a file, use block comments in the following format:

/* eslint-disable */

alert('foo');

/* eslint-enable */

You can also disable or enable warnings for specific rules:

/* eslint-disable no-alert, no-console */

alert('foo');
console.log('bar');

/* eslint-enable no-alert, no-console */

Note: /* eslint-enable */ without any specific rules listed causes all disabled rules to be re-enabled.

To disable rule warnings in an entire file, put a /* eslint-disable */ block comment at the top of the file:

/* eslint-disable */

alert('foo');

You can also disable or enable specific rules for an entire file:

/* eslint-disable no-alert */

alert('foo');

To ensure that a rule is never applied (regardless of any future enable/disable lines):

/* eslint no-alert: "off" */

alert('foo');

To disable all rules on a specific line, use a line or block comment in one of the following formats:

alert('foo'); // eslint-disable-line

// eslint-disable-next-line
alert('foo');

/* eslint-disable-next-line */
alert('foo');

alert('foo'); /* eslint-disable-line */

To disable a specific rule on a specific line:

alert('foo'); // eslint-disable-line no-alert

// eslint-disable-next-line no-alert
alert('foo');

alert('foo'); /* eslint-disable-line no-alert */

/* eslint-disable-next-line no-alert */
alert('foo');

To disable multiple rules on a specific line:

alert('foo'); // eslint-disable-line no-alert, quotes, semi

// eslint-disable-next-line no-alert, quotes, semi
alert('foo');

alert('foo'); /* eslint-disable-line no-alert, quotes, semi */

/* eslint-disable-next-line no-alert, quotes, semi */
alert('foo');

/* eslint-disable-next-line
  no-alert,
  quotes,
  semi
*/
alert('foo');

All of the above methods also work for plugin rules. For example, to disable eslint-plugin-example’s rule-name rule, combine the plugin’s name (example) and the rule’s name (rule-name) into example/rule-name:

foo(); // eslint-disable-line example/rule-name
foo(); /* eslint-disable-line example/rule-name */

Note: Comments that disable warnings for a portion of a file tell ESLint not to report rule violations for the disabled code. ESLint still parses the entire file, however, so disabled code still needs to be syntactically valid JavaScript.

Comment descriptions

Configuration comments can include descriptions to explain why disabling or re-enabling the rule is necessary. The description must come after the configuration and needs to be separated from the configuration by two or more consecutive - characters. For example:

// eslint-disable-next-line no-console -- Here's a description about why this configuration is necessary.
console.log('hello');

/* eslint-disable-next-line no-console --
 * Here's a very long description about why this configuration is necessary
 * along with some additional information
**/
console.log('hello');

Using configuration files

To disable rules inside of a configuration file for a group of files, use the overrides key along with a files key. For example:

{
  "rules": {...},
  "overrides": [
    {
      "files": ["*-test.js","*.spec.js"],
      "rules": {
        "no-unused-expressions": "off"
      }
    }
  ]
}

Disabling Inline Comments

To disable all inline config comments, use the noInlineConfig setting in your configuration file. For example:

{
  "rules": {...},
  "noInlineConfig": true
}

You can also use the –no-inline-config CLI option to disable rule comments, in addition to other in-line configuration.

Report unused eslint-disable comments

To report unused eslint-disable comments, use the reportUnusedDisableDirectives setting. For example:

{
  "rules": {...},
  "reportUnusedDisableDirectives": true
}

This setting is similar to –report-unused-disable-directives CLI option, but doesn’t fail linting (reports as "warn" severity).