noExcessiveStatementsPerFunction (JavaScript)

Language JavaScript (and super languages)

Caution

This rule is part of the nursery group. This means that it is experimental and the behavior can change at any time.

Summary

• Rule available since: v2.6.0
• Diagnostic Category: lint/nursery/noExcessiveStatementsPerFunction
• This rule doesn’t have a fix.
• The default severity of this rule is warning.
• Sources:
  • Same as max-statements

How to configure

biome.json

{
  "linter": {
    "rules": {
      "nursery": {
        "noExcessiveStatementsPerFunction": "error"
      }
    }
  }
}

Description

Enforce a maximum number of statements allowed in a function.

Functions with many statements tend to do too many things at once, which makes them harder to read, test, and maintain.

The rule checks every kind of function: function declarations and expressions, arrow functions, methods, getters, setters, and constructors.

The rule counts every statement in the function body, including the statements inside braces ({ }), such as the body of an if statement, a loop, or a try/catch. A statement without braces, such as b in if (a) b;, or a statement in a switch case, doesn’t add to the count. The statements of a nested function count towards the nested function only.

Class static blocks (static { } inside a class) aren’t checked, and their statements don’t count towards the function that contains the class.

Examples

Invalid

function foo() {
    const foo1 = 1;
    const foo2 = 2;
    const foo3 = 3;
    const foo4 = 4;
    const foo5 = 5;
    const foo6 = 6;
    const foo7 = 7;
    const foo8 = 8;
    const foo9 = 9;
    const foo10 = 10;
    const foo11 = 11;
}

code-block.js:1:1 lint/nursery/noExcessiveStatementsPerFunction ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This function has too many statements (11). Maximum allowed is 10.
  
  > 1 │ function foo() {
      │ ^^^^^^^^^^^^^^
    2 │     const foo1 = 1;
    3 │     const foo2 = 2;
  
  ℹ Functions with many statements are harder to read, test, and maintain.
  
  ℹ Consider splitting this function into smaller functions.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  

function foo(items) {
    const result = [];
    for (const item of items) {
        if (item.enabled) {
            const value = item.value;
            const label = item.label;
            const description = item.description;
            result.push({ value, label, description });
        } else {
            const fallback = item.fallback;
            const reason = item.reason;
            result.push({ fallback, reason });
        }
    }
    return result;
}

code-block.js:1:1 lint/nursery/noExcessiveStatementsPerFunction ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This function has too many statements (11). Maximum allowed is 10.
  
  > 1 │ function foo(items) {
      │ ^^^^^^^^^^^^^^^^^^^
    2 │     const result = [];
    3 │     for (const item of items) {
  
  ℹ Functions with many statements are harder to read, test, and maintain.
  
  ℹ Consider splitting this function into smaller functions.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  

Valid

function foo() {
    const foo1 = 1;
    const foo2 = 2;
    const foo3 = 3;
    const foo4 = 4;
    const foo5 = 5;
    const foo6 = 6;
    const foo7 = 7;
    const foo8 = 8;
    const foo9 = 9;
    return function () {
        // The statements of this function don't count towards `foo`.
        let bar;
        let baz;
        return 42;
    };
}

Options

max

The maximum number of statements allowed in a function.

Default: 10

biome.json

{
  "linter": {
    "rules": {
      "nursery": {
        "noExcessiveStatementsPerFunction": {
          "level": "on",
          "options": {
            "max": 2
          }
        }
      }
    }
  }
}

Invalid

function foo() {
    const a = 1;
    const b = 2;
    return a + b;
}

code-block.js:1:1 lint/nursery/noExcessiveStatementsPerFunction ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This function has too many statements (3). Maximum allowed is 2.
  
  > 1 │ function foo() {
      │ ^^^^^^^^^^^^^^
    2 │     const a = 1;
    3 │     const b = 2;
  
  ℹ Functions with many statements are harder to read, test, and maintain.
  
  ℹ Consider splitting this function into smaller functions.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  

Valid

function foo() {
    const a = 1;
    return a + 2;
}

ignoreTopLevelFunctions

When set to true, a top-level function (a function that isn’t nested in another function) isn’t checked, as long as it’s the only top-level function in the file. This is useful for files whose code is entirely wrapped in a single function, such as (function () { ... })() or define(function () { ... }). If the file contains several top-level functions, all of them are checked.

Default: false

biome.json

{
  "linter": {
    "rules": {
      "nursery": {
        "noExcessiveStatementsPerFunction": {
          "level": "on",
          "options": {
            "max": 2,
            "ignoreTopLevelFunctions": true
          }
        }
      }
    }
  }
}

Invalid

(function () {
    const a = 1;
    const b = 2;
    const c = 3;
})();

(function () {
    const a = 1;
})();

code-block.js:1:2 lint/nursery/noExcessiveStatementsPerFunction ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This function has too many statements (3). Maximum allowed is 2.
  
  > 1 │ (function () {
      │  ^^^^^^^^^^^
    2 │     const a = 1;
    3 │     const b = 2;
  
  ℹ Functions with many statements are harder to read, test, and maintain.
  
  ℹ Consider splitting this function into smaller functions.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  

Valid

(function () {
    const a = 1;
    const b = 2;
    const c = 3;
})();

Related links

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