Versions

Formatters

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

checkstyle

Outputs results to the Checkstyle format.

Example output:

<?xml version="1.0" encoding="utf-8"?><checkstyle version="4.3"><file name="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js"><error line="1" column="10" severity="error" message="&apos;addOne&apos; is defined but never used. (no-unused-vars)" source="eslint.rules.no-unused-vars" /><error line="2" column="9" severity="error" message="Use the isNaN function to compare with NaN. (use-isnan)" source="eslint.rules.use-isnan" /><error line="3" column="16" severity="error" message="Unexpected space before unary operator &apos;++&apos;. (space-unary-ops)" source="eslint.rules.space-unary-ops" /><error line="3" column="20" severity="warning" message="Missing semicolon. (semi)" source="eslint.rules.semi" /><error line="4" column="12" severity="warning" message="Unnecessary &apos;else&apos; after &apos;return&apos;. (no-else-return)" source="eslint.rules.no-else-return" /><error line="5" column="1" severity="warning" message="Expected indentation of 8 spaces but found 6. (indent)" source="eslint.rules.indent" /><error line="5" column="7" severity="error" message="Function &apos;addOne&apos; expected a return value. (consistent-return)" source="eslint.rules.consistent-return" /><error line="5" column="13" severity="warning" message="Missing semicolon. (semi)" source="eslint.rules.semi" /><error line="7" column="2" severity="error" message="Unnecessary semicolon. (no-extra-semi)" source="eslint.rules.no-extra-semi" /></file></checkstyle>

compact

Human-readable output format. Mimics the default output of JSHint.

Example output:

/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 1, col 10, Error - 'addOne' is defined but never used. (no-unused-vars)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 2, col 9, Error - Use the isNaN function to compare with NaN. (use-isnan)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 3, col 16, Error - Unexpected space before unary operator '++'. (space-unary-ops)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 3, col 20, Warning - Missing semicolon. (semi)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 4, col 12, Warning - Unnecessary 'else' after 'return'. (no-else-return)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 5, col 1, Warning - Expected indentation of 8 spaces but found 6. (indent)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 5, col 7, Error - Function 'addOne' expected a return value. (consistent-return)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 5, col 13, Warning - Missing semicolon. (semi)
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js: line 7, col 2, Error - Unnecessary semicolon. (no-extra-semi)

9 problems

html

Outputs results to HTML. The html formatter is useful for visual presentation in the browser.

Example output:

jslint-xml

Outputs results to format compatible with the JSLint Jenkins plugin.

Example output:

<?xml version="1.0" encoding="utf-8"?><jslint><file name="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js"><issue line="1" char="10" evidence="" reason="&apos;addOne&apos; is defined but never used. (no-unused-vars)" /><issue line="2" char="9" evidence="" reason="Use the isNaN function to compare with NaN. (use-isnan)" /><issue line="3" char="16" evidence="" reason="Unexpected space before unary operator &apos;++&apos;. (space-unary-ops)" /><issue line="3" char="20" evidence="" reason="Missing semicolon. (semi)" /><issue line="4" char="12" evidence="" reason="Unnecessary &apos;else&apos; after &apos;return&apos;. (no-else-return)" /><issue line="5" char="1" evidence="" reason="Expected indentation of 8 spaces but found 6. (indent)" /><issue line="5" char="7" evidence="" reason="Function &apos;addOne&apos; expected a return value. (consistent-return)" /><issue line="5" char="13" evidence="" reason="Missing semicolon. (semi)" /><issue line="7" char="2" evidence="" reason="Unnecessary semicolon. (no-extra-semi)" /></file></jslint>

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:

{"results":[{"filePath":"/var/lib/jenkins/workspace/Releases/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},{"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},{"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":";"}},{"ruleId":"no-extra-semi","severity":2,"message":"Unnecessary semicolon.","line":7,"column":2,"nodeType":"EmptyStatement","messageId":"unexpected","endLine":7,"endColumn":3,"fix":{"range":[93,95],"text":"}"}}],"suppressedMessages":[],"errorCount":5,"fatalErrorCount":0,"warningCount":4,"fixableErrorCount":2,"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","docs":{"description":"Disallow `else` blocks after `return` statements in `if` statements","recommended":false,"url":"https://eslint.org/docs/rules/no-else-return"},"schema":[{"type":"object","properties":{"allowElseIf":{"type":"boolean","default":true}},"additionalProperties":false}],"fixable":"code","messages":{"unexpected":"Unnecessary 'else' after 'return'."}},"indent":{"type":"layout","docs":{"description":"Enforce consistent indentation","recommended":false,"url":"https://eslint.org/docs/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":{"type":"layout","docs":{"description":"Enforce consistent spacing before or after unary operators","recommended":false,"url":"https://eslint.org/docs/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":{"type":"layout","docs":{"description":"Require or disallow semicolons instead of ASI","recommended":false,"url":"https://eslint.org/docs/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"}},"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/rules/consistent-return"},"schema":[{"type":"object","properties":{"treatUndefinedAsUnspecified":{"type":"boolean","default":false}},"additionalProperties":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:

[{"filePath":"/var/lib/jenkins/workspace/Releases/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},{"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},{"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":";"}},{"ruleId":"no-extra-semi","severity":2,"message":"Unnecessary semicolon.","line":7,"column":2,"nodeType":"EmptyStatement","messageId":"unexpected","endLine":7,"endColumn":3,"fix":{"range":[93,95],"text":"}"}}],"suppressedMessages":[],"errorCount":5,"fatalErrorCount":0,"warningCount":4,"fixableErrorCount":2,"fixableWarningCount":4,"source":"function addOne(i) {\n    if (i != NaN) {\n        return i ++\n    } else {\n      return\n    }\n};"}]

junit

Outputs results to format compatible with the JUnit Jenkins plugin.

Example output:

<?xml version="1.0" encoding="utf-8"?>
<testsuites>
<testsuite package="org.eslint" time="0" tests="9" errors="9" name="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js">
<testcase time="0" name="org.eslint.no-unused-vars" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="&apos;addOne&apos; is defined but never used."><![CDATA[line 1, col 10, Error - &apos;addOne&apos; is defined but never used. (no-unused-vars)]]></failure></testcase>
<testcase time="0" name="org.eslint.use-isnan" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Use the isNaN function to compare with NaN."><![CDATA[line 2, col 9, Error - Use the isNaN function to compare with NaN. (use-isnan)]]></failure></testcase>
<testcase time="0" name="org.eslint.space-unary-ops" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Unexpected space before unary operator &apos;++&apos;."><![CDATA[line 3, col 16, Error - Unexpected space before unary operator &apos;++&apos;. (space-unary-ops)]]></failure></testcase>
<testcase time="0" name="org.eslint.semi" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Missing semicolon."><![CDATA[line 3, col 20, Warning - Missing semicolon. (semi)]]></failure></testcase>
<testcase time="0" name="org.eslint.no-else-return" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Unnecessary &apos;else&apos; after &apos;return&apos;."><![CDATA[line 4, col 12, Warning - Unnecessary &apos;else&apos; after &apos;return&apos;. (no-else-return)]]></failure></testcase>
<testcase time="0" name="org.eslint.indent" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Expected indentation of 8 spaces but found 6."><![CDATA[line 5, col 1, Warning - Expected indentation of 8 spaces but found 6. (indent)]]></failure></testcase>
<testcase time="0" name="org.eslint.consistent-return" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Function &apos;addOne&apos; expected a return value."><![CDATA[line 5, col 7, Error - Function &apos;addOne&apos; expected a return value. (consistent-return)]]></failure></testcase>
<testcase time="0" name="org.eslint.semi" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Missing semicolon."><![CDATA[line 5, col 13, Warning - Missing semicolon. (semi)]]></failure></testcase>
<testcase time="0" name="org.eslint.no-extra-semi" classname="/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems"><failure message="Unnecessary semicolon."><![CDATA[line 7, col 2, Error - Unnecessary semicolon. (no-extra-semi)]]></failure></testcase>
</testsuite>
</testsuites>

stylish

Human-readable output format. This is the default formatter.

Example output:


/var/lib/jenkins/workspace/Releases/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
  7:2   error    Unnecessary semicolon                         no-extra-semi

✖ 9 problems (5 errors, 4 warnings)
  2 errors and 4 warnings potentially fixable with the `--fix` option.

tap

Outputs results to the Test Anything Protocol (TAP) specification format.

Example output:

TAP version 13
1..1
not ok 1 - /var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js
  ---
  message: '''addOne'' is defined but never used.'
  severity: error
  data:
    line: 1
    column: 10
    ruleId: no-unused-vars
  messages:
    - message: Use the isNaN function to compare with NaN.
      severity: error
      data:
        line: 2
        column: 9
        ruleId: use-isnan
    - message: Unexpected space before unary operator '++'.
      severity: error
      data:
        line: 3
        column: 16
        ruleId: space-unary-ops
    - message: Missing semicolon.
      severity: warning
      data:
        line: 3
        column: 20
        ruleId: semi
    - message: Unnecessary 'else' after 'return'.
      severity: warning
      data:
        line: 4
        column: 12
        ruleId: no-else-return
    - message: Expected indentation of 8 spaces but found 6.
      severity: warning
      data:
        line: 5
        column: 1
        ruleId: indent
    - message: Function 'addOne' expected a return value.
      severity: error
      data:
        line: 5
        column: 7
        ruleId: consistent-return
    - message: Missing semicolon.
      severity: warning
      data:
        line: 5
        column: 13
        ruleId: semi
    - message: Unnecessary semicolon.
      severity: error
      data:
        line: 7
        column: 2
        ruleId: no-extra-semi
  ...

unix

Outputs results to a format similar to many commands in UNIX-like systems. Parsable with tools such as grep, sed, and awk.

Example output:

/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:1:10: 'addOne' is defined but never used. [Error/no-unused-vars]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:2:9: Use the isNaN function to compare with NaN. [Error/use-isnan]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:3:16: Unexpected space before unary operator '++'. [Error/space-unary-ops]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:3:20: Missing semicolon. [Warning/semi]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:4:12: Unnecessary 'else' after 'return'. [Warning/no-else-return]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:5:1: Expected indentation of 8 spaces but found 6. [Warning/indent]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:5:7: Function 'addOne' expected a return value. [Error/consistent-return]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:5:13: Missing semicolon. [Warning/semi]
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js:7:2: Unnecessary semicolon. [Error/no-extra-semi]

9 problems

visualstudio

Outputs results to format compatible with the integrated terminal of the Visual Studio IDE. When using Visual Studio, you can click on the linting results in the integrated terminal to go to the issue in the source code.

Example output:

/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(1,10): error no-unused-vars : 'addOne' is defined but never used.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(2,9): error use-isnan : Use the isNaN function to compare with NaN.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(3,16): error space-unary-ops : Unexpected space before unary operator '++'.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(3,20): warning semi : Missing semicolon.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(4,12): warning no-else-return : Unnecessary 'else' after 'return'.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(5,1): warning indent : Expected indentation of 8 spaces but found 6.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(5,7): error consistent-return : Function 'addOne' expected a return value.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(5,13): warning semi : Missing semicolon.
/var/lib/jenkins/workspace/Releases/eslint Release/eslint/fullOfProblems.js(7,2): error no-extra-semi : Unnecessary semicolon.

9 problems