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 50.

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

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 50.

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: 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: 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-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-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: 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: 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: 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: 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: 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.