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

disallow constant expressions in conditions (no-constant-condition)

A constant expression (for example, a literal) as a test condition might be a typo or development trigger for a specific behavior. For example, the following code looks as if it is not ready for production.

if (false) {
    doSomethingUnfinished();
}

Rule Details

This rule disallows constant expressions in the test condition of:

• if, for, while, or do...while statement
• ?: ternary expression

Examples of incorrect code for this rule:

/*eslint no-constant-condition: "error"*/

if (false) {
    doSomethingUnfinished();
}

if (void x) {
    doSomethingUnfinished();
}

for (;-2;) {
    doSomethingForever();
}

while (typeof x) {
    doSomethingForever();
}

do {
    doSomethingForever();
} while (x = -1);

var result = 0 ? a : b;

Examples of correct code for this rule:

/*eslint no-constant-condition: "error"*/

if (x === 0) {
    doSomething();
}

for (;;) {
    doSomethingForever();
}

while (typeof x === "undefined") {
    doSomething();
}

do {
    doSomething();
} while (x);

var result = x !== 0 ? a : b;

Options

checkLoops

Set to true by default. Setting this option to false allows constant expressions in loops.

Examples of correct code for when checkLoops is false:

/*eslint no-constant-condition: ["error", { "checkLoops": false }]*/

while (true) {
    doSomething();
    if (condition()) {
        break;
    }
};

for (;true;) {
    doSomething();
    if (condition()) {
        break;
    }
};

do {
    doSomething();
    if (condition()) {
        break;
    }
} while (true)

Source: http://eslint.org/docs/rules/

disallow constant expressions in conditions (no-constant-condition)

A constant expression (for example, a literal) as a test condition might be a typo or development trigger for a specific behavior. For example, the following code looks as if it is not ready for production.

if (false) {
    doSomethingUnfinished();
}

Rule Details

This rule disallows constant expressions in the test condition of:

• if, for, while, or do...while statement
• ?: ternary expression

Examples of incorrect code for this rule:

/*eslint no-constant-condition: "error"*/

if (false) {
    doSomethingUnfinished();
}

if (void x) {
    doSomethingUnfinished();
}

for (;-2;) {
    doSomethingForever();
}

while (typeof x) {
    doSomethingForever();
}

do {
    doSomethingForever();
} while (x = -1);

var result = 0 ? a : b;

Examples of correct code for this rule:

/*eslint no-constant-condition: "error"*/

if (x === 0) {
    doSomething();
}

for (;;) {
    doSomethingForever();
}

while (typeof x === "undefined") {
    doSomething();
}

do {
    doSomething();
} while (x);

var result = x !== 0 ? a : b;

Options

checkLoops

Set to true by default. Setting this option to false allows constant expressions in loops.

Examples of correct code for when checkLoops is false:

/*eslint no-constant-condition: ["error", { "checkLoops": false }]*/

while (true) {
    doSomething();
    if (condition()) {
        break;
    }
};

for (;true;) {
    doSomething();
    if (condition()) {
        break;
    }
};

do {
    doSomething();
    if (condition()) {
        break;
    }
} while (true)

Source: http://eslint.org/docs/rules/

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 66.

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 66.

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

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/