Formatters Reference
ESLint comes with several built-in formatters to control the appearance of the linting results, and supports third-party formatters as well.
You can specify a formatter using the --format or -f flag in the CLI. For example, --format json uses the json formatter.
The built-in formatter options are:
Example Source
Examples of each formatter were created from linting fullOfProblems.js using the .eslintrc.json configuration shown below.
fullOfProblems.js:
function addOne(i) {
if (i != NaN) {
return i ++
} else {
return
}
};
.eslintrc.json:
{
"extends": "eslint:recommended",
"rules": {
"consistent-return": 2,
"indent" : [1, 4],
"no-else-return" : 1,
"semi" : [1, "always"],
"space-unary-ops" : 2
}
}
Tests the formatters with the CLI:
npx eslint --format <Add formatter here> fullOfProblems.js
Built-In Formatter Options
html
Outputs results to HTML. The html formatter is useful for visual presentation in the browser.
Example output:
json-with-metadata
Outputs JSON-serialized results. The json-with-metadata provides the same linting results as the json formatter with additional metadata about the rules applied. The linting results are included in the results property and the rules metadata is included in the metadata property.
Alternatively, you can use the ESLint Node.js API to programmatically use ESLint.
Example output (formatted for easier reading):
{
"results": [
{
"filePath": "/var/lib/jenkins/workspace/eslint Release/eslint/fullOfProblems.js",
"messages": [
{
"ruleId": "no-unused-vars",
"severity": 2,
"message": "'addOne' is defined but never used.",
"line": 1,
"column": 10,
"nodeType": "Identifier",
"messageId": "unusedVar",
"endLine": 1,
"endColumn": 16,
"suggestions": [
{
"messageId": "removeVar",
"data": {
"varName": "addOne"
},
"fix": {
"range": [
0,
94
],
"text": ""
},
"desc": "Remove unused variable 'addOne'."
}
]
},
{
"ruleId": "use-isnan",
"severity": 2,
"message": "Use the isNaN function to compare with NaN.",
"line": 2,
"column": 9,
"nodeType": "BinaryExpression",
"messageId": "comparisonWithNaN",
"endLine": 2,
"endColumn": 17,
"suggestions": [
{
"messageId": "replaceWithIsNaN",
"fix": {
"range": [
29,
37
],
"text": "!Number.isNaN(i)"
},
"desc": "Replace with Number.isNaN."
},
{
"messageId": "replaceWithCastingAndIsNaN",
"fix": {
"range": [
29,
37
],
"text": "!Number.isNaN(Number(i))"
},
"desc": "Replace with Number.isNaN and cast to a Number."
}
]
},
{
"ruleId": "space-unary-ops",
"severity": 2,
"message": "Unexpected space before unary operator '++'.",
"line": 3,
"column": 16,
"nodeType": "UpdateExpression",
"messageId": "unexpectedBefore",
"endLine": 3,
"endColumn": 20,
"fix": {
"range": [
57,
58
],
"text": ""
}
},
{
"ruleId": "semi",
"severity": 1,
"message": "Missing semicolon.",
"line": 3,
"column": 20,
"nodeType": "ReturnStatement",
"messageId": "missingSemi",
"endLine": 4,
"endColumn": 1,
"fix": {
"range": [
60,
60
],
"text": ";"
}
},
{
"ruleId": "no-else-return",
"severity": 1,
"message": "Unnecessary 'else' after 'return'.",
"line": 4,
"column": 12,
"nodeType": "BlockStatement",
"messageId": "unexpected",
"endLine": 6,
"endColumn": 6,
"fix": {
"range": [
0,
94
],
"text": "function addOne(i) {\n if (i != NaN) {\n return i ++\n } \n return\n \n}"
}
},
{
"ruleId": "indent",
"severity": 1,
"message": "Expected indentation of 8 spaces but found 6.",
"line": 5,
"column": 1,
"nodeType": "Keyword",
"messageId": "wrongIndentation",
"endLine": 5,
"endColumn": 7,
"fix": {
"range": [
74,
80
],
"text": " "
}
},
{
"ruleId": "consistent-return",
"severity": 2,
"message": "Function 'addOne' expected a return value.",
"line": 5,
"column": 7,
"nodeType": "ReturnStatement",
"messageId": "missingReturnValue",
"endLine": 5,
"endColumn": 13
},
{
"ruleId": "semi",
"severity": 1,
"message": "Missing semicolon.",
"line": 5,
"column": 13,
"nodeType": "ReturnStatement",
"messageId": "missingSemi",
"endLine": 6,
"endColumn": 1,
"fix": {
"range": [
86,
86
],
"text": ";"
}
}
],
"suppressedMessages": [],
"errorCount": 4,
"fatalErrorCount": 0,
"warningCount": 4,
"fixableErrorCount": 1,
"fixableWarningCount": 4,
"source": "function addOne(i) {\n if (i != NaN) {\n return i ++\n } else {\n return\n }\n};"
}
],
"metadata": {
"rulesMeta": {
"no-else-return": {
"type": "suggestion",
"defaultOptions": [
{
"allowElseIf": true
}
],
"docs": {
"description": "Disallow `else` blocks after `return` statements in `if` statements",
"recommended": false,
"url": "https://eslint.org/docs/latest/rules/no-else-return"
},
"schema": [
{
"type": "object",
"properties": {
"allowElseIf": {
"type": "boolean"
}
},
"additionalProperties": false
}
],
"fixable": "code",
"messages": {
"unexpected": "Unnecessary 'else' after 'return'."
}
},
"indent": {
"deprecated": true,
"replacedBy": [],
"type": "layout",
"docs": {
"description": "Enforce consistent indentation",
"recommended": false,
"url": "https://eslint.org/docs/latest/rules/indent"
},
"fixable": "whitespace",
"schema": [
{
"oneOf": [
{
"enum": [
"tab"
]
},
{
"type": "integer",
"minimum": 0
}
]
},
{
"type": "object",
"properties": {
"SwitchCase": {
"type": "integer",
"minimum": 0,
"default": 0
},
"VariableDeclarator": {
"oneOf": [
{
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
{
"type": "object",
"properties": {
"var": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
"let": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
"const": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
}
},
"additionalProperties": false
}
]
},
"outerIIFEBody": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"off"
]
}
]
},
"MemberExpression": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"off"
]
}
]
},
"FunctionDeclaration": {
"type": "object",
"properties": {
"parameters": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
"body": {
"type": "integer",
"minimum": 0
}
},
"additionalProperties": false
},
"FunctionExpression": {
"type": "object",
"properties": {
"parameters": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
"body": {
"type": "integer",
"minimum": 0
}
},
"additionalProperties": false
},
"StaticBlock": {
"type": "object",
"properties": {
"body": {
"type": "integer",
"minimum": 0
}
},
"additionalProperties": false
},
"CallExpression": {
"type": "object",
"properties": {
"arguments": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
}
},
"additionalProperties": false
},
"ArrayExpression": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
"ObjectExpression": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
"ImportDeclaration": {
"oneOf": [
{
"type": "integer",
"minimum": 0
},
{
"enum": [
"first",
"off"
]
}
]
},
"flatTernaryExpressions": {
"type": "boolean",
"default": false
},
"offsetTernaryExpressions": {
"type": "boolean",
"default": false
},
"ignoredNodes": {
"type": "array",
"items": {
"type": "string",
"not": {
"pattern": ":exit$"
}
}
},
"ignoreComments": {
"type": "boolean",
"default": false
}
},
"additionalProperties": false
}
],
"messages": {
"wrongIndentation": "Expected indentation of but found ."
}
},
"space-unary-ops": {
"deprecated": true,
"replacedBy": [],
"type": "layout",
"docs": {
"description": "Enforce consistent spacing before or after unary operators",
"recommended": false,
"url": "https://eslint.org/docs/latest/rules/space-unary-ops"
},
"fixable": "whitespace",
"schema": [
{
"type": "object",
"properties": {
"words": {
"type": "boolean",
"default": true
},
"nonwords": {
"type": "boolean",
"default": false
},
"overrides": {
"type": "object",
"additionalProperties": {
"type": "boolean"
}
}
},
"additionalProperties": false
}
],
"messages": {
"unexpectedBefore": "Unexpected space before unary operator ''.",
"unexpectedAfter": "Unexpected space after unary operator ''.",
"unexpectedAfterWord": "Unexpected space after unary word operator ''.",
"wordOperator": "Unary word operator '' must be followed by whitespace.",
"operator": "Unary operator '' must be followed by whitespace.",
"beforeUnaryExpressions": "Space is required before unary expressions ''."
}
},
"semi": {
"deprecated": true,
"replacedBy": [],
"type": "layout",
"docs": {
"description": "Require or disallow semicolons instead of ASI",
"recommended": false,
"url": "https://eslint.org/docs/latest/rules/semi"
},
"fixable": "code",
"schema": {
"anyOf": [
{
"type": "array",
"items": [
{
"enum": [
"never"
]
},
{
"type": "object",
"properties": {
"beforeStatementContinuationChars": {
"enum": [
"always",
"any",
"never"
]
}
},
"additionalProperties": false
}
],
"minItems": 0,
"maxItems": 2
},
{
"type": "array",
"items": [
{
"enum": [
"always"
]
},
{
"type": "object",
"properties": {
"omitLastInOneLineBlock": {
"type": "boolean"
},
"omitLastInOneLineClassBody": {
"type": "boolean"
}
},
"additionalProperties": false
}
],
"minItems": 0,
"maxItems": 2
}
]
},
"messages": {
"missingSemi": "Missing semicolon.",
"extraSemi": "Extra semicolon."
}
},
"consistent-return": {
"type": "suggestion",
"docs": {
"description": "Require `return` statements to either always or never specify values",
"recommended": false,
"url": "https://eslint.org/docs/latest/rules/consistent-return"
},
"schema": [
{
"type": "object",
"properties": {
"treatUndefinedAsUnspecified": {
"type": "boolean"
}
},
"additionalProperties": false
}
],
"defaultOptions": [
{
"treatUndefinedAsUnspecified": false
}
],
"messages": {
"missingReturn": "Expected to return a value at the end of .",
"missingReturnValue": " expected a return value.",
"unexpectedReturnValue": " expected no return value."
}
}
}
}
}
json
Outputs JSON-serialized results. The json formatter is useful when you want to programmatically work with the CLI's linting results.
Alternatively, you can use the ESLint Node.js API to programmatically use ESLint.
Example output (formatted for easier reading):
[
{
"filePath": "/var/lib/jenkins/workspace/eslint Release/eslint/fullOfProblems.js",
"messages": [
{
"ruleId": "no-unused-vars",
"severity": 2,
"message": "'addOne' is defined but never used.",
"line": 1,
"column": 10,
"nodeType": "Identifier",
"messageId": "unusedVar",
"endLine": 1,
"endColumn": 16,
"suggestions": [
{
"messageId": "removeVar",
"data": {
"varName": "addOne"
},
"fix": {
"range": [
0,
94
],
"text": ""
},
"desc": "Remove unused variable 'addOne'."
}
]
},
{
"ruleId": "use-isnan",
"severity": 2,
"message": "Use the isNaN function to compare with NaN.",
"line": 2,
"column": 9,
"nodeType": "BinaryExpression",
"messageId": "comparisonWithNaN",
"endLine": 2,
"endColumn": 17,
"suggestions": [
{
"messageId": "replaceWithIsNaN",
"fix": {
"range": [
29,
37
],
"text": "!Number.isNaN(i)"
},
"desc": "Replace with Number.isNaN."
},
{
"messageId": "replaceWithCastingAndIsNaN",
"fix": {
"range": [
29,
37
],
"text": "!Number.isNaN(Number(i))"
},
"desc": "Replace with Number.isNaN and cast to a Number."
}
]
},
{
"ruleId": "space-unary-ops",
"severity": 2,
"message": "Unexpected space before unary operator '++'.",
"line": 3,
"column": 16,
"nodeType": "UpdateExpression",
"messageId": "unexpectedBefore",
"endLine": 3,
"endColumn": 20,
"fix": {
"range": [
57,
58
],
"text": ""
}
},
{
"ruleId": "semi",
"severity": 1,
"message": "Missing semicolon.",
"line": 3,
"column": 20,
"nodeType": "ReturnStatement",
"messageId": "missingSemi",
"endLine": 4,
"endColumn": 1,
"fix": {
"range": [
60,
60
],
"text": ";"
}
},
{
"ruleId": "no-else-return",
"severity": 1,
"message": "Unnecessary 'else' after 'return'.",
"line": 4,
"column": 12,
"nodeType": "BlockStatement",
"messageId": "unexpected",
"endLine": 6,
"endColumn": 6,
"fix": {
"range": [
0,
94
],
"text": "function addOne(i) {\n if (i != NaN) {\n return i ++\n } \n return\n \n}"
}
},
{
"ruleId": "indent",
"severity": 1,
"message": "Expected indentation of 8 spaces but found 6.",
"line": 5,
"column": 1,
"nodeType": "Keyword",
"messageId": "wrongIndentation",
"endLine": 5,
"endColumn": 7,
"fix": {
"range": [
74,
80
],
"text": " "
}
},
{
"ruleId": "consistent-return",
"severity": 2,
"message": "Function 'addOne' expected a return value.",
"line": 5,
"column": 7,
"nodeType": "ReturnStatement",
"messageId": "missingReturnValue",
"endLine": 5,
"endColumn": 13
},
{
"ruleId": "semi",
"severity": 1,
"message": "Missing semicolon.",
"line": 5,
"column": 13,
"nodeType": "ReturnStatement",
"messageId": "missingSemi",
"endLine": 6,
"endColumn": 1,
"fix": {
"range": [
86,
86
],
"text": ";"
}
}
],
"suppressedMessages": [],
"errorCount": 4,
"fatalErrorCount": 0,
"warningCount": 4,
"fixableErrorCount": 1,
"fixableWarningCount": 4,
"source": "function addOne(i) {\n if (i != NaN) {\n return i ++\n } else {\n return\n }\n};"
}
]
stylish
Human-readable output format. This is the default formatter.
Example output:
/var/lib/jenkins/workspace/eslint Release/eslint/fullOfProblems.js
1:10 error 'addOne' is defined but never used no-unused-vars
2:9 error Use the isNaN function to compare with NaN use-isnan
3:16 error Unexpected space before unary operator '++' space-unary-ops
3:20 warning Missing semicolon semi
4:12 warning Unnecessary 'else' after 'return' no-else-return
5:1 warning Expected indentation of 8 spaces but found 6 indent
5:7 error Function 'addOne' expected a return value consistent-return
5:13 warning Missing semicolon semi
✖ 8 problems (4 errors, 4 warnings)
1 error and 4 warnings potentially fixable with the `--fix` option.