func-params.md

enforce the number of parameters used in a function definition or expression (func-params)

This rule allows you to set a max limit for the number of parameters used in function definitions, function expressions, and arrow function expressions. It allows you to set a global limit, and to override this global limit for each of the types (definitions and expressions).

Rule Details

By design, this plugin's rules don't have pre-set defaults. So, you've to configure this rule as described here in order to use it. Noting that all the options are used as keys in a single config object (no arrays or nested objects).

Options

Here are the available options for this rule:

• global: accepts an integer indicating the max number of parameters used in a function definition or expression. This applies to all types unless overridden for a specific type

• funcDefinition: accepts an integer indicating the max number of parameters used in a function definition. This overrides the global limit

• funcExpression: accepts an integer indicating the max number of parameters used in a function expression. This overrides the global limit

• arrowFuncExpression: accepts an integer indicating the max number of parameters used in an arrow function expression. This overrides the global limit

• funcTypeAnnotation: accepts an integer indicating the max number of parameters used in a TypeScript function type annotation. This overrides the global limit

If you have a need to set the value of an option to 0, it is a valid limit that's supported by this rule.

If you want to disable this rule (removing all restrictions) for any of the options, you can set its value to -1. For example, setting an option like "arrowFuncExpression": -1 in the config, allows you to use arrow functions with any number of parameters (basically from 0 to an unlimited number of parameters). This overrides the global limit.

Error message examples:

• function 'foo' has too many parameters (3). Maximum allowed is (1).
• arrow function 'b' has too many parameters (3). Maximum allowed is (1).
• arrow function has too many parameters (3). Maximum allowed is (1).
• function 'onBar' has too many parameters (3). Maximum allowed is (1). [TS key in interface or object type]
• function 'onBarFn' has too many parameters (3). Maximum allowed is (1). [TS function type alias]
• function 'myFunction' has too many parameters (3). Maximum allowed is (1). [TS method signature]

Example (A)

With a config like:

{
  "rules": {
    "func-params-args/func-params": [
      "warn",
      {
        "global": 3,
        "arrowFuncExpression": 4
      }
    ]
  }
}

Examples of incorrect code for this rule:

function foo(param1, param2, param3, param4) {}

a = function (param1, param2, param3, param4) {};

b = (param1, param2, param3, param4, param5) => {};

c = async function (param1, param2, param3, param4) {};

c.reduce((param1, param2, param3, param4, param5) => {});

interface IFoo {
  onBar: (
    param1: string,
    param2: string,
    param3: string,
    param4: string,
  ) => void;
}

type FooType = {
  onBar: (
    param1: number,
    param2: number,
    param3: number,
    param4: number,
  ) => void;
};

type onBarFn = (
  param1: number,
  param2: number,
  param3: number,
  param4: number,
) => void;

interface MyInterface {
  myFunction(
    param1: string,
    param2: string,
    param3: string,
    param4: string,
  ): void;
}

const func2: (
  param1: string,
  param2: string,
  param3: string,
  param3: string,
) => void = (arg1, arg2, arg3, arg4) => {};

Examples of correct code for this rule:

function foo(param1, param2, param3) {}

a = function (param1, param2, param3) {};

b = (param1, param2, param3, param4) => {};

c.reduce((param1, param2, param3, param4) => {});

function foo(param1) {}

a = function (param1, param2) {};

b = () => {};

c.reduce((param1, param2, param3) => {});

interface IFoo {
  onBar: (param1: string, param2: string, param3: string) => void;
}

type FooType = {
  onBar: (param1: number, param2: number, param3: number) => void;
};

type onBarFn = (param1: number, param2: number, param3: number) => void;

Example (B)

With a config like:

{
  "rules": {
    "func-params-args/func-params": [
      "warn",
      {
        "funcDefinition": 1,
        "funcExpression": 2
      }
    ]
  }
}

Examples of incorrect code for this rule:

function foo(param1, param2) {}

a = function (param1, param2, param3) {};

Examples of correct code for this rule:

function foo(param1) {}

a = function (param1, param2) {};

// No restrictions below on arrow function expressions
// since the 'global' option is not configured

b = (param1, param2, param3, param4, param5) => {};

c = () => {};

c.reduce((param1, param2, param3, param4) => {});