Rule: ban-comma-operator

Disallows the comma operator to be used.

Read more about the comma operator here.

Rationale

Using the comma operator can create a potential for many non-obvious bugs or lead to misunderstanding of code.

Examples

foo((bar, baz)); // evaluates to 'foo(baz)' because of the extra parens - confusing and not obvious

switch (foo) {
    case 1, 2: // equals 'case 2' - probably intended 'case 1: case2:'
        return true;
    case 3:
        return false;
}

let x = (y = 1, z = 2); // x is equal to 2 - this may not be immediately obvious.

Examples

"ban-comma-operator": true

For more information see this page.

Rule: semicolon

Enforces consistent semicolon usage at the end of every statement.

Notes

• Has Fix

Config

One of the following arguments must be provided:

• "always" enforces semicolons at the end of every statement.
• "never" disallows semicolons at the end of every statement except for when they are necessary.

The following arguments may be optionally provided:

• "ignore-interfaces" skips checking semicolons at the end of interface members.
• "ignore-bound-class-methods" skips checking semicolons at the end of bound class methods.
• "strict-bound-class-methods" disables any special handling of bound class methods and treats them as any other assignment. This option overrides "ignore-bound-class-methods".

Examples

"semicolon": true,always

"semicolon": true,never

"semicolon": true,always,ignore-interfaces

"semicolon": true,always,ignore-bound-class-methods

Schema

{
  "type": "array",
  "items": [
    {
      "type": "string",
      "enum": [
        "always",
        "never"
      ]
    },
    {
      "type": "string",
      "enum": [
        "ignore-interfaces"
      ]
    }
  ],
  "additionalItems": false
}

For more information see this page.

Rule: whitespace

Enforces whitespace style conventions.

Rationale

Helps maintain a readable, consistent style in your codebase.

Notes

• Has Fix

Config

Several arguments may be optionally provided:

• "check-branch" checks branching statements (if/else/for/while) are followed by whitespace.
• "check-decl"checks that variable declarations have whitespace around the equals token.
• "check-operator" checks for whitespace around operator tokens.
• "check-module" checks for whitespace in import & export statements.
• "check-separator" checks for whitespace after separator tokens (,/;).
• "check-rest-spread" checks that there is no whitespace after rest/spread operator (...).
• "check-type" checks for whitespace before a variable type specification.
• "check-typecast" checks for whitespace between a typecast and its target.
• "check-type-operator" checks for whitespace between type operators | and &.
• "check-preblock" checks for whitespace before the opening brace of a block.
• "check-postbrace" checks for whitespace after an opening brace.

Examples

"whitespace": true,check-branch,check-operator,check-typecast

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "check-branch",
      "check-decl",
      "check-operator",
      "check-module",
      "check-separator",
      "check-rest-spread",
      "check-type",
      "check-typecast",
      "check-type-operator",
      "check-preblock",
      "check-postbrace"
    ]
  },
  "minLength": 0,
  "maxLength": 11
}

For more information see this page.

Rule: whitespace

Enforces whitespace style conventions.

Rationale

Helps maintain a readable, consistent style in your codebase.

Notes

• Has Fix

Config

Several arguments may be optionally provided:

• "check-branch" checks branching statements (if/else/for/while) are followed by whitespace.
• "check-decl"checks that variable declarations have whitespace around the equals token.
• "check-operator" checks for whitespace around operator tokens.
• "check-module" checks for whitespace in import & export statements.
• "check-separator" checks for whitespace after separator tokens (,/;).
• "check-rest-spread" checks that there is no whitespace after rest/spread operator (...).
• "check-type" checks for whitespace before a variable type specification.
• "check-typecast" checks for whitespace between a typecast and its target.
• "check-type-operator" checks for whitespace between type operators | and &.
• "check-preblock" checks for whitespace before the opening brace of a block.
• "check-postbrace" checks for whitespace after an opening brace.

Examples

"whitespace": true,check-branch,check-operator,check-typecast

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "check-branch",
      "check-decl",
      "check-operator",
      "check-module",
      "check-separator",
      "check-rest-spread",
      "check-type",
      "check-typecast",
      "check-type-operator",
      "check-preblock",
      "check-postbrace"
    ]
  },
  "minLength": 0,
  "maxLength": 11
}

For more information see this page.

Rule: semicolon

Enforces consistent semicolon usage at the end of every statement.

Notes

• Has Fix

Config

One of the following arguments must be provided:

• "always" enforces semicolons at the end of every statement.
• "never" disallows semicolons at the end of every statement except for when they are necessary.

The following arguments may be optionally provided:

• "ignore-interfaces" skips checking semicolons at the end of interface members.
• "ignore-bound-class-methods" skips checking semicolons at the end of bound class methods.
• "strict-bound-class-methods" disables any special handling of bound class methods and treats them as any other assignment. This option overrides "ignore-bound-class-methods".

Examples

"semicolon": true,always

"semicolon": true,never

"semicolon": true,always,ignore-interfaces

"semicolon": true,always,ignore-bound-class-methods

Schema

{
  "type": "array",
  "items": [
    {
      "type": "string",
      "enum": [
        "always",
        "never"
      ]
    },
    {
      "type": "string",
      "enum": [
        "ignore-interfaces"
      ]
    }
  ],
  "additionalItems": false
}

For more information see this page.

Rule: radix

Requires the radix parameter to be specified when calling parseInt.

Rationale

From MDN:

Always specify this parameter to eliminate reader confusion and to guarantee predictable behavior. Different implementations produce different results when a radix is not specified, usually defaulting the value to 10.

Config

Not configurable.

Examples

"radix": true

For more information see this page.

Rule: no-unused-expression

Disallows unused expression statements.

Unused expressions are expression statements which are not assignments or function calls (and thus usually no-ops).

Rationale

Detects potential errors where an assignment or function call was intended.

Config

Three arguments may be optionally provided:

• allow-fast-null-checks allows to use logical operators to perform fast null checks and perform method or function calls for side effects (e.g. e && e.preventDefault()).
• allow-new allows 'new' expressions for side effects (e.g. new ModifyGlobalState();.
• allow-tagged-template allows tagged templates for side effects (e.g. this.add\foo`;`.

Examples

"no-unused-expression": true

"no-unused-expression": true,allow-fast-null-checks

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-fast-null-checks",
      "allow-new",
      "allow-tagged-template"
    ]
  },
  "minLength": 0,
  "maxLength": 3
}

For more information see this page.

Rule: no-unused-expression

Disallows unused expression statements.

Unused expressions are expression statements which are not assignments or function calls (and thus usually no-ops).

Rationale

Detects potential errors where an assignment or function call was intended.

Config

Three arguments may be optionally provided:

• allow-fast-null-checks allows to use logical operators to perform fast null checks and perform method or function calls for side effects (e.g. e && e.preventDefault()).
• allow-new allows 'new' expressions for side effects (e.g. new ModifyGlobalState();.
• allow-tagged-template allows tagged templates for side effects (e.g. this.add\foo`;`.

Examples

"no-unused-expression": true

"no-unused-expression": true,allow-fast-null-checks

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-fast-null-checks",
      "allow-new",
      "allow-tagged-template"
    ]
  },
  "minLength": 0,
  "maxLength": 3
}

For more information see this page.

Rule: no-return-await

Disallows unnecessary return await.

Rationale

An async function always wraps the return value in a Promise. Using return await just adds extra time before the overreaching promise is resolved without changing the semantics.

Notes

• Has Fix

Config

Not configurable.

Examples

"no-return-await": true

For more information see this page.

Rule: semicolon

Enforces consistent semicolon usage at the end of every statement.

Notes

• Has Fix

Config

One of the following arguments must be provided:

• "always" enforces semicolons at the end of every statement.
• "never" disallows semicolons at the end of every statement except for when they are necessary.

The following arguments may be optionally provided:

• "ignore-interfaces" skips checking semicolons at the end of interface members.
• "ignore-bound-class-methods" skips checking semicolons at the end of bound class methods.
• "strict-bound-class-methods" disables any special handling of bound class methods and treats them as any other assignment. This option overrides "ignore-bound-class-methods".

Examples

"semicolon": true,always

"semicolon": true,never

"semicolon": true,always,ignore-interfaces

"semicolon": true,always,ignore-bound-class-methods

Schema

{
  "type": "array",
  "items": [
    {
      "type": "string",
      "enum": [
        "always",
        "never"
      ]
    },
    {
      "type": "string",
      "enum": [
        "ignore-interfaces"
      ]
    }
  ],
  "additionalItems": false
}

For more information see this page.

Rule: whitespace

Enforces whitespace style conventions.

Rationale

Helps maintain a readable, consistent style in your codebase.

Notes

• Has Fix

Config

Several arguments may be optionally provided:

• "check-branch" checks branching statements (if/else/for/while) are followed by whitespace.
• "check-decl"checks that variable declarations have whitespace around the equals token.
• "check-operator" checks for whitespace around operator tokens.
• "check-module" checks for whitespace in import & export statements.
• "check-separator" checks for whitespace after separator tokens (,/;).
• "check-rest-spread" checks that there is no whitespace after rest/spread operator (...).
• "check-type" checks for whitespace before a variable type specification.
• "check-typecast" checks for whitespace between a typecast and its target.
• "check-type-operator" checks for whitespace between type operators | and &.
• "check-preblock" checks for whitespace before the opening brace of a block.
• "check-postbrace" checks for whitespace after an opening brace.

Examples

"whitespace": true,check-branch,check-operator,check-typecast

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "check-branch",
      "check-decl",
      "check-operator",
      "check-module",
      "check-separator",
      "check-rest-spread",
      "check-type",
      "check-typecast",
      "check-type-operator",
      "check-preblock",
      "check-postbrace"
    ]
  },
  "minLength": 0,
  "maxLength": 11
}

For more information see this page.

Rule: semicolon

Enforces consistent semicolon usage at the end of every statement.

Notes

• Has Fix

Config

One of the following arguments must be provided:

• "always" enforces semicolons at the end of every statement.
• "never" disallows semicolons at the end of every statement except for when they are necessary.

The following arguments may be optionally provided:

• "ignore-interfaces" skips checking semicolons at the end of interface members.
• "ignore-bound-class-methods" skips checking semicolons at the end of bound class methods.
• "strict-bound-class-methods" disables any special handling of bound class methods and treats them as any other assignment. This option overrides "ignore-bound-class-methods".

Examples

"semicolon": true,always

"semicolon": true,never

"semicolon": true,always,ignore-interfaces

"semicolon": true,always,ignore-bound-class-methods

Schema

{
  "type": "array",
  "items": [
    {
      "type": "string",
      "enum": [
        "always",
        "never"
      ]
    },
    {
      "type": "string",
      "enum": [
        "ignore-interfaces"
      ]
    }
  ],
  "additionalItems": false
}

For more information see this page.

Rule: radix

Requires the radix parameter to be specified when calling parseInt.

Rationale

From MDN:

Always specify this parameter to eliminate reader confusion and to guarantee predictable behavior. Different implementations produce different results when a radix is not specified, usually defaulting the value to 10.

Config

Not configurable.

Examples

"radix": true

For more information see this page.

Rule: no-unused-expression

Disallows unused expression statements.

Unused expressions are expression statements which are not assignments or function calls (and thus usually no-ops).

Rationale

Detects potential errors where an assignment or function call was intended.

Config

Three arguments may be optionally provided:

• allow-fast-null-checks allows to use logical operators to perform fast null checks and perform method or function calls for side effects (e.g. e && e.preventDefault()).
• allow-new allows 'new' expressions for side effects (e.g. new ModifyGlobalState();.
• allow-tagged-template allows tagged templates for side effects (e.g. this.add\foo`;`.

Examples

"no-unused-expression": true

"no-unused-expression": true,allow-fast-null-checks

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-fast-null-checks",
      "allow-new",
      "allow-tagged-template"
    ]
  },
  "minLength": 0,
  "maxLength": 3
}

For more information see this page.

Rule: semicolon

Enforces consistent semicolon usage at the end of every statement.

Notes

• Has Fix

Config

One of the following arguments must be provided:

• "always" enforces semicolons at the end of every statement.
• "never" disallows semicolons at the end of every statement except for when they are necessary.

The following arguments may be optionally provided:

• "ignore-interfaces" skips checking semicolons at the end of interface members.
• "ignore-bound-class-methods" skips checking semicolons at the end of bound class methods.
• "strict-bound-class-methods" disables any special handling of bound class methods and treats them as any other assignment. This option overrides "ignore-bound-class-methods".

Examples

"semicolon": true,always

"semicolon": true,never

"semicolon": true,always,ignore-interfaces

"semicolon": true,always,ignore-bound-class-methods

Schema

{
  "type": "array",
  "items": [
    {
      "type": "string",
      "enum": [
        "always",
        "never"
      ]
    },
    {
      "type": "string",
      "enum": [
        "ignore-interfaces"
      ]
    }
  ],
  "additionalItems": false
}

For more information see this page.

Rule: no-unused-expression

Disallows unused expression statements.

Unused expressions are expression statements which are not assignments or function calls (and thus usually no-ops).

Rationale

Detects potential errors where an assignment or function call was intended.

Config

Three arguments may be optionally provided:

• allow-fast-null-checks allows to use logical operators to perform fast null checks and perform method or function calls for side effects (e.g. e && e.preventDefault()).
• allow-new allows 'new' expressions for side effects (e.g. new ModifyGlobalState();.
• allow-tagged-template allows tagged templates for side effects (e.g. this.add\foo`;`.

Examples

"no-unused-expression": true

"no-unused-expression": true,allow-fast-null-checks

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-fast-null-checks",
      "allow-new",
      "allow-tagged-template"
    ]
  },
  "minLength": 0,
  "maxLength": 3
}

For more information see this page.

Rule: whitespace

Enforces whitespace style conventions.

Rationale

Helps maintain a readable, consistent style in your codebase.

Notes

• Has Fix

Config

Several arguments may be optionally provided:

• "check-branch" checks branching statements (if/else/for/while) are followed by whitespace.
• "check-decl"checks that variable declarations have whitespace around the equals token.
• "check-operator" checks for whitespace around operator tokens.
• "check-module" checks for whitespace in import & export statements.
• "check-separator" checks for whitespace after separator tokens (,/;).
• "check-rest-spread" checks that there is no whitespace after rest/spread operator (...).
• "check-type" checks for whitespace before a variable type specification.
• "check-typecast" checks for whitespace between a typecast and its target.
• "check-type-operator" checks for whitespace between type operators | and &.
• "check-preblock" checks for whitespace before the opening brace of a block.
• "check-postbrace" checks for whitespace after an opening brace.

Examples

"whitespace": true,check-branch,check-operator,check-typecast

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "check-branch",
      "check-decl",
      "check-operator",
      "check-module",
      "check-separator",
      "check-rest-spread",
      "check-type",
      "check-typecast",
      "check-type-operator",
      "check-preblock",
      "check-postbrace"
    ]
  },
  "minLength": 0,
  "maxLength": 11
}

For more information see this page.

Rule: no-return-await

Disallows unnecessary return await.

Rationale

An async function always wraps the return value in a Promise. Using return await just adds extra time before the overreaching promise is resolved without changing the semantics.

Notes

• Has Fix

Config

Not configurable.

Examples

"no-return-await": true

For more information see this page.

Rule: label-position

Only allows labels in sensible locations.

This rule only allows labels to be on do/for/while/switch statements.

Rationale

Labels in JavaScript only can be used in conjunction with break or continue, constructs meant to be used for loop flow control. While you can theoretically use labels on any block statement in JS, it is considered poor code structure to do so.

Config

Not configurable.

Examples

"label-position": true

For more information see this page.

Rule: no-unused-expression

Disallows unused expression statements.

Unused expressions are expression statements which are not assignments or function calls (and thus usually no-ops).

Rationale

Detects potential errors where an assignment or function call was intended.

Config

Three arguments may be optionally provided:

• allow-fast-null-checks allows to use logical operators to perform fast null checks and perform method or function calls for side effects (e.g. e && e.preventDefault()).
• allow-new allows 'new' expressions for side effects (e.g. new ModifyGlobalState();.
• allow-tagged-template allows tagged templates for side effects (e.g. this.add\foo`;`.

Examples

"no-unused-expression": true

"no-unused-expression": true,allow-fast-null-checks

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-fast-null-checks",
      "allow-new",
      "allow-tagged-template"
    ]
  },
  "minLength": 0,
  "maxLength": 3
}

For more information see this page.