This past year we’ve seen an incredible growth coming from ESLint, a linter on steroids for ECMAScript, JSX and JavaScript code. It quickly became the go-to JavaScript linter for the programming language’s community. The work of Nicholas and the
numerous
contributors is really impressive.
The original philosophy behind the tool is something that speaks to us greatly as it is completely pluggable. ESLint makes it
very easy
to write your own plugins and share them with the community. You can find several examples on
NPM
.
Today I’m happy to announce that ESLint rules are now supported on Codacy. Here are the rules taken from the
rules list
that you can now enforce on Codacy. Enable them on your projects and share your feedback with us!
ESLint Rules
Possible Errors
The following rules point out areas where you might have made mistakes.
comma-dangle
— disallow or enforce trailing commas (recommended)
no-cond-assign
— disallow assignment in conditional expressions (recommended)
no-console
— disallow use of console in the node environment (recommended)
no-constant-condition
— disallow use of constant expressions in conditions (recommended)
no-control-regex
— disallow control characters in regular expressions (recommended)
no-debugger
— disallow use of debugger (recommended)
no-dupe-args
— disallow duplicate arguments in functions (recommended)
no-dupe-keys
— disallow duplicate keys when creating object literals (recommended)
no-duplicate-case
— disallow a duplicate case label. (recommended)
no-empty-character-class
— disallow the use of empty character classes in regular expressions (recommended)
no-empty
— disallow empty statements (recommended)
no-ex-assign
— disallow assigning to the exception in a catch block (recommended)
no-extra-boolean-cast
— disallow double-negation boolean casts in a boolean context (recommended)
no-extra-parens
— disallow unnecessary parentheses
no-extra-semi
— disallow unnecessary semicolons (recommended) (fixable)
no-func-assign
— disallow overwriting functions written as function declarations (recommended)
no-inner-declarations
— disallow function or variable declarations in nested blocks (recommended)
no-invalid-regexp
— disallow invalid regular expression strings in the RegExp constructor (recommended)
no-irregular-whitespace
— disallow irregular whitespace outside of strings and comments (recommended)
no-negated-in-lhs
— disallow negation of the left operand of an in expression (recommended)
no-obj-calls
— disallow the use of object properties of the global object (Math and JSON) as functions (recommended)
no-regex-spaces
— disallow multiple spaces in a regular expression literal (recommended)
no-sparse-arrays
— disallow sparse arrays (recommended)
no-unexpected-multiline
— Avoid code that looks like two expressions but is actually one
no-unreachable
— disallow unreachable statements after a return, throw, continue, or break statement (recommended)
use-isnan
— disallow comparisons with the value NaN (recommended)
valid-jsdoc
— Ensure JSDoc comments are valid
valid-typeof
— Ensure that the results of typeof are compared against a valid string (recommended)
Best Practices
These are rules designed to prevent you from making mistakes. They either prescribe a better way of doing something or help you avoid footguns.
accessor-pairs
— Enforces getter/setter pairs in objects
block-scoped-var
— treat var statements as if they were block scoped
complexity
— specify the maximum cyclomatic complexity allowed in a program
consistent-return
— require return statements to either always or never specify values
curly
— specify curly brace conventions for all control statements
default-case
— require default case in switch statements
dot-location
— enforces consistent newlines before or after dots
dot-notation
— encourages use of dot notation whenever possible
eqeqeq
— require the use of === and !== (fixable)
guard-for-in
— make sure for-in loops have an if statement
no-alert
— disallow the use of alert, confirm, and prompt
no-caller
— disallow use of arguments.caller or arguments.callee
no-case-declarations
— disallow lexical declarations in case clauses
no-div-regex
— disallow division operators explicitly at beginning of regular expression
no-else-return
— disallow else after a return in an if
no-empty-label
— disallow use of labels for anything other than loops and switches
no-empty-pattern
— disallow use of empty destructuring patterns
no-eq-null
— disallow comparisons to null without a type-checking operator
no-eval
— disallow use of eval()
no-extend-native
— disallow adding to native types
no-extra-bind
— disallow unnecessary function binding
no-fallthrough
— disallow fallthrough of case statements (recommended)
no-floating-decimal
— disallow the use of leading or trailing decimal points in numeric literals
no-implicit-coercion
— disallow the type conversions with shorter notations
no-implied-eval
— disallow use of eval()-like methods
no-invalid-this
— disallow this keywords outside of classes or class-like objects
no-iterator
— disallow usage of __iterator__ property
no-labels
— disallow use of labeled statements
no-lone-blocks
— disallow unnecessary nested blocks
no-loop-func
— disallow creation of functions within loops
no-magic-numbers
— disallow the use of magic numbers
no-multi-spaces
— disallow use of multiple spaces (fixable)
no-multi-str
— disallow use of multiline strings
no-native-reassign
— disallow reassignments of native objects
no-new-func
— disallow use of new operator for Function object
no-new-wrappers
— disallows creating new instances of String,Number, and Boolean
no-new
— disallow use of the new operator when not part of an assignment or comparison
no-octal
— disallow use of octal literals (recommended)
no-param-reassign
— disallow reassignment of function parameters
no-process-env
— disallow use of process.env
no-proto
— disallow usage of __proto__ property
no-redeclare
— disallow declaring the same variable more than once (recommended)
no-return-assign
— disallow use of assignment in return statement
no-script-url
— disallow use of javascript: urls.
no-self-compare
— disallow comparisons where both sides are exactly the same
no-sequences
— disallow use of the comma operator
no-throw-literal
— restrict what can be thrown as an exception
no-unused-expressions
— disallow usage of expressions in statement position
no-useless-call
— disallow unnecessary .call() and .apply()
no-useless-concat
— disallow unnecessary concatenation of literals or template literals
no-void
— disallow use of the void operator
no-warning-comments
— disallow usage of configurable warning terms in comments — e.g. TODO or FIXME
no-with
— disallow use of the with statement
radix
— require use of the second argument for parseInt()
vars-on-top
— require declaration of all vars at the top of their containing scope
wrap-iife
— require immediate function invocation to be wrapped in parentheses
yoda
— require or disallow Yoda conditions
Strict Mode
These rules relate to using strict mode.
strict
— controls location of Use Strict Directives
Variables
These rules have to do with variable declarations.
init-declarations
— enforce or disallow variable initializations at definition
no-catch-shadow
— disallow the catch clause parameter name being the same as a variable in the outer scope
no-delete-var
— disallow deletion of variables (recommended)
no-label-var
— disallow labels that share a name with a variable
no-shadow-restricted-names
— disallow shadowing of names such as arguments
no-shadow
— disallow declaration of variables already declared in the outer scope
no-undef-init
— disallow use of undefined when initializing variables
no-undef
— disallow use of undeclared variables unless mentioned in a /*global */ block (recommended)
no-undefined
— disallow use of undefined variable
no-unused-vars
— disallow declaration of variables that are not used in the code (recommended)
no-use-before-define
— disallow use of variables before they are defined
Node.js and CommonJS
These rules are specific to JavaScript running on Node.js or using CommonJS in the browser.
callback-return
— enforce return after a callback
global-require
— enforce require() on top-level module scope
handle-callback-err
— enforce error handling in callbacks
no-mixed-requires
— disallow mixing regular variable and require declarations
no-new-require
— disallow use of new operator with the require function
no-path-concat
— disallow string concatenation with __dirname and __filename
no-process-exit
— disallow process.exit()
no-restricted-modules
— restrict usage of specified node modules
no-sync
— disallow use of synchronous methods
Stylistic Issues
These rules are purely matters of style and are quite subjective.
array-bracket-spacing
— enforce spacing inside array brackets (fixable)
block-spacing
— disallow or enforce spaces inside of single line blocks (fixable)
brace-style
— enforce one true brace style
camelcase
— require camel case names
comma-spacing
— enforce spacing before and after comma (fixable)
comma-style
— enforce one true comma style
computed-property-spacing
— require or disallow padding inside computed properties (fixable)
consistent-this
— enforce consistent naming when capturing the current execution context
eol-last
— enforce newline at the end of file, with no multiple empty lines (fixable)
func-names
— require function expressions to have a name
func-style
— enforce use of function declarations or expressions
id-length
— this option enforces minimum and maximum identifier lengths (variable names, property names etc.)
id-match
— require identifiers to match the provided regular expression
indent
— specify tab or space width for your code (fixable)
jsx-quotes
— specify whether double or single quotes should be used in JSX attributes
key-spacing
— enforce spacing between keys and values in object literal properties
linebreak-style
— disallow mixed ‘LF’ and ‘CRLF’ as linebreaks
lines-around-comment
— enforce empty lines around comments
max-depth
— specify the maximum depth that blocks can be nested
max-len
— specify the maximum length of a line in your program
max-nested-callbacks
— specify the maximum depth callbacks can be nested
max-params
— limits the number of parameters that can be used in the function declaration.
max-statements
— specify the maximum number of statement allowed in a function
new-cap
— require a capital letter for constructors
new-parens
— disallow the omission of parentheses when invoking a constructor with no arguments
newline-after-var
— require or disallow an empty newline after variable declarations
no-array-constructor
— disallow use of the Array constructor
no-bitwise
— disallow use of bitwise operators
no-continue
— disallow use of the continue statement
no-inline-comments
— disallow comments inline after code
no-lonely-if
— disallow if as the only statement in an else block
no-mixed-spaces-and-tabs
— disallow mixed spaces and tabs for indentation (recommended)
no-multiple-empty-lines
— disallow multiple empty lines
no-negated-condition
— disallow negated conditions
no-nested-ternary
— disallow nested ternary expressions
no-new-object
— disallow the use of the Object constructor
no-plusplus
— disallow use of unary operators, ++ and —
no-restricted-syntax
— disallow use of certain syntax in code
no-spaced-func
— disallow space between function identifier and application (fixable)
no-ternary
— disallow the use of ternary operators
no-trailing-spaces
— disallow trailing whitespace at the end of lines (fixable)
no-underscore-dangle
— disallow dangling underscores in identifiers
no-unneeded-ternary
— disallow the use of ternary operators when a simpler alternative exists
object-curly-spacing
— require or disallow padding inside curly braces (fixable)
one-var
— require or disallow one variable declaration per function
operator-assignment
— require assignment operator shorthand where possible or prohibit it entirely
operator-linebreak
— enforce operators to be placed before or after line breaks
padded-blocks
— enforce padding within blocks
quote-props
— require quotes around object literal property names
quotes
— specify whether backticks, double or single quotes should be used (fixable)
require-jsdoc
— Require JSDoc comment
semi-spacing
— enforce spacing before and after semicolons
semi
— require or disallow use of semicolons instead of ASI (fixable)
sort-vars
— sort variables within the same declaration block
space-after-keywords
— require a space after certain keywords (fixable)
space-before-blocks
— require or disallow a space before blocks (fixable)
space-before-function-paren
— require or disallow a space before function opening parentheses (fixable)
space-before-keywords
— require a space before certain keywords (fixable)
space-in-parens
— require or disallow spaces inside parentheses
space-infix-ops
— require spaces around operators (fixable)
space-return-throw-case
— require a space after return, throw, and case (fixable)
space-unary-ops
— require or disallow spaces before/after unary operators (fixable)
spaced-comment
— require or disallow a space immediately following the // or /* in a comment
wrap-regex
— require regex literals to be wrapped in parentheses
ECMAScript 6
These rules are only relevant to ES6 environments.
arrow-body-style
— require braces in arrow function body
arrow-parens
— require parentheses in arrow function arguments
arrow-spacing
— require space before/after arrow function’s arrow (fixable)
constructor-super
— verify calls of super() in constructors
generator-star-spacing
— enforce spacing around the * in generator functions (fixable)
no-arrow-condition
— disallow arrow functions where a condition is expected
no-class-assign
— disallow modifying variables of class declarations
no-const-assign
— disallow modifying variables that are declared using const
no-dupe-class-members
— disallow duplicate name in class members
no-this-before-super
— disallow use of this/super before calling super() in constructors.
no-var
— require let or const instead of var
object-shorthand
— require method and property shorthand syntax for object literals
prefer-arrow-callback
— suggest using arrow functions as callbacks
prefer-const
— suggest using const declaration for variables that are never modified after declared
prefer-reflect
— suggest using Reflect methods where applicable
prefer-spread
— suggest using the spread operator instead of .apply().
prefer-template
— suggest using template literals instead of strings concatenation
require-yield
— disallow generator functions that do not have yield
Edit: We just published an ebook: “
The Ultimate Guide to Code Review
” based on a survey of 680+ developers. Enjoy!
For more on ESLint from us check out our
ESLint archive
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