.eslintrc.js

"use strict";

module.exports = {
  env: {
    node: true,
    es6: true,
  },

  extends: ["prettier"],

  parserOptions: {
    ecmaVersion: 9,
  },

  globals: {
    fetch: false,
    WebAssembly: false,
  },

  rules: {
    // Always require spacing around a single line block
    "block-spacing": "error",

    // Warn about cyclomatic complexity in functions.
    // XXX Get this down to 20?
    complexity: ["error", 25],

    // Functions must always return something or nothing
    "consistent-return": "error",

    // Require braces around blocks that start a new line
    curly: ["error", "multi-line"],

    // Encourage the use of dot notation whenever possible.
    "dot-notation": "error",

    // Always require a trailing EOL
    "eol-last": "error",

    // Unix linebreaks
    "linebreak-style": ["error", "unix"],

    // Don't enforce the maximum depth that blocks can be nested. The complexity
    // rule is a better rule to check this.
    "max-depth": "off",

    // Maximum depth callbacks can be nested.
    "max-nested-callbacks": ["error", 10],

    // Always require parenthesis for new calls
    "new-parens": "error",

    // Use [] instead of Array()
    "no-array-constructor": "error",

    // Disallow use of arguments.caller or arguments.callee.
    "no-caller": "error",

    // Disallow modifying variables of class declarations.
    "no-class-assign": "error",

    // Disallow assignment operators in conditional statements
    "no-cond-assign": "error",

    // Disallow modifying variables that are declared using const.
    "no-const-assign": "error",

    // Disallow control characters in regular expressions.
    "no-control-regex": "error",

    // Disallow the use of debugger
    "no-debugger": "error",

    // Disallow deleting variables
    "no-delete-var": "error",

    // No duplicate arguments in function declarations
    "no-dupe-args": "error",

    // Disallow duplicate class members.
    "no-dupe-class-members": "error",

    // No duplicate keys in object declarations
    "no-dupe-keys": "error",

    // No duplicate cases in switch statements
    "no-duplicate-case": "error",

    // If an if block ends with a return no need for an else block
    "no-else-return": "error",

    // No empty statements
    "no-empty": ["error", { allowEmptyCatch: true }],

    // No empty character classes in regex
    "no-empty-character-class": "error",

    // Disallow empty destructuring
    "no-empty-pattern": "error",

    // Disallow eval and setInteral/setTimeout with strings
    "no-eval": "error",

    // No assigning to exception variable
    "no-ex-assign": "error",

    // Disallow unnecessary calls to .bind()
    "no-extra-bind": "error",

    // No using !! where casting to boolean is already happening
    "no-extra-boolean-cast": "error",

    // No overwriting defined functions
    "no-func-assign": "error",

    // Disallow eval and setInteral/setTimeout with strings
    "no-implied-eval": "error",

    // No invalid regular expressions
    "no-invalid-regexp": "error",

    // No odd whitespace characters
    "no-irregular-whitespace": "error",

    // Disallow the use of the __iterator__ property
    "no-iterator": "error",

    // No labels
    "no-labels": "error",

    // Disallow unnecessary nested blocks
    "no-lone-blocks": "error",

    // No single if block inside an else block
    "no-lonely-if": "error",

    // No unnecessary spacing
    "no-multi-spaces": [
      "error",
      {
        exceptions: {
          ArrayExpression: true,
          AssignmentExpression: true,
          ObjectExpression: true,
          VariableDeclarator: true,
        },
      },
    ],

    // No reassigning native JS objects
    "no-native-reassign": "error",

    // Nested ternary statements are confusing
    "no-nested-ternary": "error",

    // Use {} instead of new Object()
    "no-new-object": "error",

    // Dissallow use of new wrappers
    "no-new-wrappers": "error",

    // No Math() or JSON()
    "no-obj-calls": "error",

    // No octal literals
    "no-octal": "error",

    // No redeclaring variables
    "no-redeclare": "error",

    // Disallow multiple spaces in regular expressions
    "no-regex-spaces": "error",

    // Disallows unnecessary `return await ...`.
    "no-return-await": "error",

    // Disallow assignments where both sides are exactly the same
    "no-self-assign": "error",

    // No unnecessary comparisons
    "no-self-compare": "error",

    // No declaring variables from an outer scope
    "no-shadow": "error",

    // No declaring variables that hide things like arguments
    "no-shadow-restricted-names": "error",

    // Disallow sparse arrays
    "no-sparse-arrays": "error",

    // Disallow tabs.
    "no-tabs": "error",

    // No using undeclared variables
    "no-undef": "error",

    // Error on newline where a semicolon is needed
    "no-unexpected-multiline": "error",

    // Disallow the use of Boolean literals in conditional expressions.
    "no-unneeded-ternary": "error",

    // No unreachable statements
    "no-unreachable": "error",

    // Disallow control flow statements in finally blocks
    "no-unsafe-finally": "error",

    // No (!foo in bar) or (!object instanceof Class)
    "no-unsafe-negation": "error",

    // No declaring variables that are never used
    "no-unused-vars": [
      "error",
      {
        args: "none",
        vars: "local",
      },
    ],

    // No using variables before defined
    "no-use-before-define": ["error", "nofunc"],

    // Disallow unnecessary .call() and .apply()
    "no-useless-call": "error",

    // Don't concatenate string literals together (unless they span multiple
    // lines)
    "no-useless-concat": "error",

    // Disallow redundant return statements
    "no-useless-return": "error",

    // Use const or let instead of var
    "no-var": "error",

    // No using with
    "no-with": "error",

    // Require object-literal shorthand with ES6 method syntax
    "object-shorthand": ["error", "always", { avoidQuotes: true }],

    // Use const instead of let where possible
    "prefer-const": "error",

    // Require space before blocks
    "space-before-blocks": "error",

    // Requires or disallows a whitespace (space or tab) beginning a comment
    "spaced-comment": "error",

    // No comparisons to NaN
    "use-isnan": "error",

    // Only check typeof against valid results
    "valid-typeof": "error",

    "max-len": ["error", { code: 120, ignoreUrls: true }],
  },
};