noUnusedVariables (since v0.9.0)

This rule is recommended by Rome.

Disallow unused variables.

Examples

Invalid

const a = 4;

error[js/noUnusedVariables]: This variable is unused.
  ┌─ js/noUnusedVariables.js:1:7
  │
1 │ const a = 4;
  │       ^

=  note: Unused variables usually are result of incomplete refactoring, typos and other source of bugs.

let a = 4;

error[js/noUnusedVariables]: This variable is unused.
  ┌─ js/noUnusedVariables.js:1:5
  │
1 │ let a = 4;
  │     ^

=  note: Unused variables usually are result of incomplete refactoring, typos and other source of bugs.

function foo() {
};

error[js/noUnusedVariables]: This function is unused.
  ┌─ js/noUnusedVariables.js:1:10
  │
1 │ function foo() {
  │          ^^^

=  note: Unused variables usually are result of incomplete refactoring, typos and other source of bugs.

function foo(myVar) {
    console.log('foo');
}
foo();

error[js/noUnusedVariables]: This parameter is unused.
  ┌─ js/noUnusedVariables.js:1:14
  │
1 │ function foo(myVar) {
  │              ^^^^^

=  note: Unused variables usually are result of incomplete refactoring, typos and other source of bugs.

const foo = () => {
};

error[js/noUnusedVariables]: This variable is unused.
  ┌─ js/noUnusedVariables.js:1:7
  │
1 │ const foo = () => {
  │       ^^^

=  note: Unused variables usually are result of incomplete refactoring, typos and other source of bugs.

function foo() {
    foo();
}

error[js/noUnusedVariables]: This function is unused.
  ┌─ js/noUnusedVariables.js:1:10
  │
1 │ function foo() {
  │          ^^^

=  note: Unused variables usually are result of incomplete refactoring, typos and other source of bugs.

const foo = () => {
    foo();
    console.log(this);
};

error[js/noUnusedVariables]: This variable is unused.
  ┌─ js/noUnusedVariables.js:1:7
  │
1 │ const foo = () => {
  │       ^^^

=  note: Unused variables usually are result of incomplete refactoring, typos and other source of bugs.

Valid

function foo(b) {
    console.log(b)
};
foo();

function foo(_unused) {
};
foo();

import React from 'react';
function foo() {
    return <div />;
};
foo();

function used_overloaded(): number;
function used_overloaded(s: string): string;
function used_overloaded(s?: string) {
    return s;
}
used_overloaded();