no-empty-pattern.md

title	rule_type
no-empty-pattern	problem

When using destructuring, it's possible to create a pattern that has no effect. This happens when empty curly braces are used to the right of an embedded object destructuring pattern, such as:

// doesn't create any variables
var {a: {}} = foo;

In this code, no new variables are created because a is just a location helper while the {} is expected to contain the variables to create, such as:

// creates variable b
var {a: { b }} = foo;

In many cases, the empty object pattern is a mistake where the author intended to use a default value instead, such as:

// creates variable a
var {a = {}} = foo;

The difference between these two patterns is subtle, especially because the problematic empty pattern looks just like an object literal.

Rule Details

This rule aims to flag any empty patterns in destructured objects and arrays, and as such, will report a problem whenever one is encountered.

Examples of incorrect code for this rule:

::: incorrect

/*eslint no-empty-pattern: "error"*/

var {} = foo;
var [] = foo;
var {a: {}} = foo;
var {a: []} = foo;
function foo({}) {}
function foo([]) {}
function foo({a: {}}) {}
function foo({a: []}) {}

:::

Examples of correct code for this rule:

::: correct

/*eslint no-empty-pattern: "error"*/

var {a = {}} = foo;
var {a = []} = foo;
function foo({a = {}}) {}
function foo({a = []}) {}

:::

Options

This rule has an object option for exceptions:

allowObjectPatternsAsParameters

Set to false by default. Setting this option to true allows empty object patterns as function parameters.

Note: This rule doesn't allow empty array patterns as function parameters.

Examples of incorrect code for this rule with the {"allowObjectPatternsAsParameters": true} option:

::: incorrect

/*eslint no-empty-pattern: ["error", { "allowObjectPatternsAsParameters": true }]*/

function foo({a: {}}) {}
var foo = function({a: {}}) {};
var foo = ({a: {}}) => {};
var foo = ({} = bar) => {};
var foo = ({} = { bar: 1 }) => {};

function foo([]) {}

:::

Examples of correct code for this rule with the {"allowObjectPatternsAsParameters": true} option:

::: correct

/*eslint no-empty-pattern: ["error", { "allowObjectPatternsAsParameters": true }]*/

function foo({}) {}
var foo = function({}) {};
var foo = ({}) => {};

function foo({} = {}) {}

:::