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

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 60.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

Rule: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

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: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

For more information see this page.

Rule: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

For more information see this page.

Rule: object-literal-shorthand

Enforces/disallows use of ES6 object literal shorthand.

Notes

• Has Fix

Config

"always" assumed to be default option, thus with no options provided the rule enforces object literal methods and properties shorthands. With "never" option provided, any shorthand object literal syntax causes an error.

The rule can be configured in a more granular way. With {"property": "never"} provided (which is equivalent to {"property": "never", "method": "always"}), the rule only flags property shorthand assignments, and respectively with {"method": "never"} (equivalent to {"property": "always", "method": "never"}), the rule fails only on method shorthands.

Examples

"object-literal-shorthand": true

"object-literal-shorthand": true,never

"object-literal-shorthand": true,[object Object]

Schema

{
  "oneOf": [
    {
      "type": "string",
      "enum": [
        "never"
      ]
    },
    {
      "type": "object",
      "properties": {
        "property": {
          "type": "string",
          "enum": [
            "never"
          ]
        },
        "method": {
          "type": "string",
          "enum": [
            "never"
          ]
        }
      },
      "minProperties": 1,
      "maxProperties": 2
    }
  ]
}

For more information see this page.

Rule: comment-format

Enforces formatting rules for single-line comments.

Rationale

Helps maintain a consistent, readable style in your codebase.

Notes

• Has Fix

Config

Four arguments may be optionally provided:

• "check-space" requires that all single-line comments must begin with a space, as in // comment
  • note that for comments starting with multiple slashes, e.g. ///, leading slashes are ignored
  • TypeScript reference comments are ignored completely
• "check-lowercase" requires that the first non-whitespace character of a comment must be lowercase, if applicable.
• "check-uppercase" requires that the first non-whitespace character of a comment must be uppercase, if applicable.
• "allow-trailing-lowercase" allows that only the first comment of a series of comments needs to be uppercase.
  • requires "check-uppercase"
  • comments must start at the same position

Exceptions to "check-lowercase" or "check-uppercase" can be managed with object that may be passed as last argument.

One of two options can be provided in this object:

• "ignore-words" - array of strings - words that will be ignored at the beginning of the comment.
• "ignore-pattern" - string - RegExp pattern that will be ignored at the beginning of the comment.

Examples

"comment-format": true,check-space,check-uppercase,allow-trailing-lowercase

"comment-format": true,check-lowercase,[object Object]

"comment-format": true,check-lowercase,[object Object]

Schema

{
  "type": "array",
  "items": {
    "anyOf": [
      {
        "type": "string",
        "enum": [
          "check-space",
          "check-lowercase",
          "check-uppercase",
          "allow-trailing-lowercase"
        ]
      },
      {
        "type": "object",
        "properties": {
          "ignore-words": {
            "type": "array",
            "items": {
              "type": "string"
            }
          },
          "ignore-pattern": {
            "type": "string"
          }
        },
        "minProperties": 1,
        "maxProperties": 1
      }
    ]
  },
  "minLength": 1,
  "maxLength": 5
}

For more information see this page.

Rule: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

For more information see this page.

Rule: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

For more information see this page.

Rule: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

For more information see this page.

Rule: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

For more information see this page.

Rule: quotemark

Enforces quote character for string literals.

Notes

• Has Fix

Config

Five arguments may be optionally provided:

• "single" enforces single quotes.
• "double" enforces double quotes.
• "backtick" enforces backticks.
• "jsx-single" enforces single quotes for JSX attributes.
• "jsx-double" enforces double quotes for JSX attributes.
• "avoid-template" forbids single-line untagged template strings that do not contain string interpolations. Note that backticks may still be used if "avoid-escape" is enabled and both single and double quotes are present in the string (the latter option takes precedence).
• "avoid-escape" allows you to use the "other" quotemark in cases where escaping would normally be required. For example, [true, "double", "avoid-escape"] would not report a failure on the string literal 'Hello "World"'.

Examples

"quotemark": true,single,avoid-escape,avoid-template

"quotemark": true,single,jsx-double

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "single",
      "double",
      "backtick",
      "jsx-single",
      "jsx-double",
      "avoid-escape",
      "avoid-template"
    ]
  },
  "minLength": 0,
  "maxLength": 5
}

For more information see this page.

Rule: no-empty-interface

Forbids empty interfaces.

Rationale

An empty interface is equivalent to its supertype (or {}).

Notes

• TypeScript Only

Config

Not configurable.

For more information see this page.