complexity

Enforce a maximum cyclomatic complexity allowed in a program

Cyclomatic complexity measures the number of linearly independent paths through a program’s source code. This rule allows setting a cyclomatic complexity threshold.

function a(x) {
    if (true) {
        return x; // 1st path
    } else if (false) {
        return x+1; // 2nd path
    } else {
        return 4; // 3rd path
    }
}
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Rule Details

This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20).

Examples of incorrect code for a maximum of 2:

Open in Playground

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else if (false) {
        return x+1;
    } else {
        return 4; // 3rd path
    }
}

function b() {
    foo ||= 1;
    bar &&= 1;
}

function c(a = {}) { // default parameter -> 2nd path
    const { b = 'default' } = a; // default value during destructuring -> 3rd path
}

function d(a) {
    return a?.b?.c; // optional chaining with two optional properties creates two additional branches
}
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Examples of correct code for a maximum of 2:

Open in Playground

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else {
        return 4;
    }
}

function b() {
    foo ||= 1;
}
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Class field initializers and class static blocks are implicit functions. Therefore, their complexity is calculated separately for each initializer and each static block, and it doesn’t contribute to the complexity of the enclosing code.

Examples of additional incorrect code for a maximum of 2:

Open in Playground

/*eslint complexity: ["error", 2]*/

class C {
    x = a || b || c; // this initializer has complexity = 3
}

class D { // this static block has complexity = 3
    static {
        if (foo) {
            bar = baz || qux;
        }
    }
}
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Examples of additional correct code for a maximum of 2:

Open in Playground

/*eslint complexity: ["error", 2]*/

function foo() { // this function has complexity = 1
    class C {
        x = a + b; // this initializer has complexity = 1
        y = c || d; // this initializer has complexity = 2
        z = e && f; // this initializer has complexity = 2

        static p = g || h; // this initializer has complexity = 2
        static q = i ? j : k; // this initializer has complexity = 2

        static { // this static block has complexity = 2
            if (foo) {
                baz = bar;
            }
        }

        static { // this static block has complexity = 2
            qux = baz || quux;
        }
    }
}
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Options

This rule has a number or object option:

"max" (default: 20) enforces a maximum complexity
"variant": "classic" | "modified" (default: "classic") cyclomatic complexity variant to use

max

Customize the threshold with the max property.

"complexity": ["error", { "max": 2 }]
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Deprecated: the object property maximum is deprecated. Please use the property max instead.

Or use the shorthand syntax:

"complexity": ["error", 2]
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variant

Cyclomatic complexity variant to use:

"classic" (default) - Classic McCabe cyclomatic complexity
"modified" - Modified cyclomatic complexity

Modified cyclomatic complexity is the same as the classic cyclomatic complexity, but each switch statement only increases the complexity value by 1, regardless of how many case statements it contains.

Examples of correct code for this rule with the { "max": 3, "variant": "modified" } option:

Open in Playground

/*eslint complexity: ["error", {"max": 3, "variant": "modified"}]*/

function a(x) {     // initial modified complexity is 1
    switch (x) {    // switch statement increases modified complexity by 1
        case 1:
            1;
            break;
        case 2:
            2;
            break;
        case 3:
            if (x === 'foo') {  // if block increases modified complexity by 1
                3;
            }
            break;
        default:
            4;
    }
}
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