max-params

Enforce a maximum number of parameters in function definitions

Functions that take numerous parameters can be difficult to read and write because it requires the memorization of what each parameter is, its type, and the order they should appear in. As a result, many coders adhere to a convention that caps the number of parameters a function can take.

function foo (bar, baz, qux, qxx) { // four parameters, may be too many
    doSomething();
}
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Rule Details

This rule enforces a maximum number of parameters allowed in function definitions.

Options

This rule has a number or object option:

• "max" (default 3) enforces a maximum number of parameters in function definitions
• "countThis" (default "except-void", possible values "always", "never" or "except-void") whether to count a this declaration (TypeScript only)

Deprecated: The object property maximum is deprecated; please use the object property max instead. Deprecated: The object property countVoidThis is deprecated; please use countThis: "except-void" instead of countVoidThis: false, and countThis: "always" instead of countVoidThis: true.

max

Examples of incorrect code for this rule with the default { "max": 3 } option:

/*eslint max-params: ["error", 3]*/

function foo1 (bar, baz, qux, qxx) {
    doSomething();
}

let foo2 = (bar, baz, qux, qxx) => {
    doSomething();
};
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Examples of correct code for this rule with the default { "max": 3 } option:

/*eslint max-params: ["error", 3]*/

function foo1 (bar, baz, qux) {
    doSomething();
}

let foo2 = (bar, baz, qux) => {
    doSomething();
};
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countThis (TypeScript only)

This rule has a TypeScript-specific option countThis that allows you to count a this declaration. Valid values are:

• "always": any this type annotation will count as a parameter
• "never": this won’t ever be counted
• "except-void": this will be counted only if its type is not void. Equivalent to the deprecated countVoidThis: false.

Examples of correct TypeScript code for this rule:

/*eslint max-params: ["error", { "max": 2, "countThis": "except-void" }]*/

function hasNoThis(this: void, first: string, second: string) {
	// ...
}
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/*eslint max-params: ["error", { "max": 2, "countThis": "never" }]*/

function hasThis(this: unknown[], first: string, second: string) {
	// ...
}
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Examples of incorrect TypeScript code for this rule:

/*eslint max-params: ["error", { "max": 2, "countThis": "always" }]*/

function hasNoThis(this: void, first: string, second: string) {
	// ...
}
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/*eslint max-params: ["error", { "max": 2, "countThis": "except-void" }]*/

function hasThis(this: unknown[], first: string, second: string) {
	// ...
}
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Related Rules

• complexity
• max-depth
• max-len
• max-lines
• max-lines-per-function
• max-nested-callbacks
• max-statements

Version

This rule was introduced in ESLint v0.0.9.

Resources

• Rule source
• Tests source