Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

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: prefer-for-of

Recommends a 'for-of' loop over a standard 'for' loop if the index is only used to access the array being iterated.

Rationale

A for(... of ...) loop is easier to implement and read when the index is not needed.

Config

Not configurable.

Examples

"prefer-for-of": 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: 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: 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: 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: 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: 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.