Rule: only-arrow-functions

Disallows traditional (non-arrow) function expressions.

Note that non-arrow functions are allowed if 'this' appears somewhere in its body (as such functions cannot be converted to arrow functions).

Rationale

Traditional functions don't bind lexical scope, which can lead to unexpected behavior when accessing 'this'.

Config

Two arguments may be optionally provided:

• "allow-declarations" allows standalone function declarations.
• "allow-named-functions" allows the expression function foo() {} but not function() {}.

Examples

"only-arrow-functions": true

"only-arrow-functions": true,allow-declarations,allow-named-functions

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-declarations",
      "allow-named-functions"
    ]
  },
  "minLength": 0,
  "maxLength": 1
}

For more information see this page.

Rule: prefer-const

Requires that variable declarations use const instead of let and var if possible.

If a variable is only assigned to once when it is declared, it should be declared using 'const'

Notes

• Has Fix

Config

An optional object containing the property "destructuring" with two possible values:

• "any" (default) - If any variable in destructuring can be const, this rule warns for those variables.
• "all" - Only warns if all variables in destructuring can be const.

Examples

"prefer-const": true

"prefer-const": true,[object Object]

Schema

{
  "type": "object",
  "properties": {
    "destructuring": {
      "type": "string",
      "enum": [
        "all",
        "any"
      ]
    }
  }
}

For more information see this page.

Rule: eofline

Ensures the file ends with a newline.

Fix for single-line files is not supported.

Rationale

It is a standard convention to end files with a newline.

Notes

• Has Fix

Config

Not configurable.

Examples

"eofline": true

For more information see this page.

Rule: no-bitwise

Disallows bitwise operators.

Specifically, the following bitwise operators are banned: &, &=, |, |=, ^, ^=, <<, <<=, >>, >>=, >>>, >>>=, and ~. This rule does not ban the use of & and | for intersection and union types.

Rationale

Bitwise operators are often typos - for example bool1 & bool2 instead of bool1 && bool2. They also can be an indicator of overly clever code which decreases maintainability.

Config

Not configurable.

Examples

"no-bitwise": true

For more information see this page.

Rule: one-variable-per-declaration

Disallows multiple variable definitions in the same declaration statement.

Config

One argument may be optionally provided:

• ignore-for-loop allows multiple variable definitions in a for loop declaration.

Examples

"one-variable-per-declaration": true

"one-variable-per-declaration": true,ignore-for-loop

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "ignore-for-loop"
    ]
  },
  "minLength": 0,
  "maxLength": 1
}

For more information see this page.

Rule: no-bitwise

Disallows bitwise operators.

Specifically, the following bitwise operators are banned: &, &=, |, |=, ^, ^=, <<, <<=, >>, >>=, >>>, >>>=, and ~. This rule does not ban the use of & and | for intersection and union types.

Rationale

Bitwise operators are often typos - for example bool1 & bool2 instead of bool1 && bool2. They also can be an indicator of overly clever code which decreases maintainability.

Config

Not configurable.

Examples

"no-bitwise": true

For more information see this page.

Rule: no-var-keyword

Disallows usage of the var keyword.

Use let or const instead.

Rationale

Declaring variables using var has several edge case behaviors that make var unsuitable for modern code. Variables declared by var have their parent function block as their scope, ignoring other control flow statements. vars have declaration "hoisting" (similar to functions) and can appear to be used before declaration.

Variables declared by const and let instead have as their scope the block in which they are defined, and are not allowed to used before declaration or be re-declared with another const or let.

Notes

• Has Fix

Config

Not configurable.

Examples

"no-var-keyword": true

For more information see this page.

Rule: no-bitwise

Disallows bitwise operators.

Specifically, the following bitwise operators are banned: &, &=, |, |=, ^, ^=, <<, <<=, >>, >>=, >>>, >>>=, and ~. This rule does not ban the use of & and | for intersection and union types.

Rationale

Bitwise operators are often typos - for example bool1 & bool2 instead of bool1 && bool2. They also can be an indicator of overly clever code which decreases maintainability.

Config

Not configurable.

Examples

"no-bitwise": true

For more information see this page.

Rule: triple-equals

Requires === and !== in place of == and !=.

Config

Two arguments may be optionally provided:

• "allow-null-check" allows == and != when comparing to null.
• "allow-undefined-check" allows == and != when comparing to undefined.

Examples

"triple-equals": true

"triple-equals": true,allow-null-check

"triple-equals": true,allow-undefined-check

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-null-check",
      "allow-undefined-check"
    ]
  },
  "minLength": 0,
  "maxLength": 2
}

For more information see this page.

Rule: prefer-const

Requires that variable declarations use const instead of let and var if possible.

If a variable is only assigned to once when it is declared, it should be declared using 'const'

Notes

• Has Fix

Config

An optional object containing the property "destructuring" with two possible values:

• "any" (default) - If any variable in destructuring can be const, this rule warns for those variables.
• "all" - Only warns if all variables in destructuring can be const.

Examples

"prefer-const": true

"prefer-const": true,[object Object]

Schema

{
  "type": "object",
  "properties": {
    "destructuring": {
      "type": "string",
      "enum": [
        "all",
        "any"
      ]
    }
  }
}

For more information see this page.