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no-lone-blocks

Disallow unnecessary nested blocks

In JavaScript, prior to ES6, standalone code blocks delimited by curly braces do not create a new scope and have no use. For example, these curly braces do nothing to foo:

{
var foo = bar();
}

In ES6, code blocks may create a new scope if a block-level binding (let and const), a class declaration or a function declaration (in strict mode) are present. A block is not considered redundant in these cases.

Rule Details

This rule aims to eliminate unnecessary and potentially confusing blocks at the top level of a script or within other blocks.

Examples of incorrect code for this rule:

/*eslint no-lone-blocks: "error"*/

{}

if (foo) {
bar();
{
baz();
}
}

function bar() {
{
baz();
}
}

{
function foo() {}
}

{
aLabel: {
}
}

class C {
static {
{
foo();
}
}
}

Examples of correct code for this rule with ES6 environment:

/*eslint no-lone-blocks: "error"*/
/*eslint-env es6*/

while (foo) {
bar();
}

if (foo) {
if (bar) {
baz();
}
}

function bar() {
baz();
}

{
let x = 1;
}

{
const y = 1;
}

{
class Foo {}
}

aLabel: {
}

class C {
static {
lbl: {
if (something) {
break lbl;
}

foo();
}
}
}

Examples of correct code for this rule with ES6 environment and strict mode via "parserOptions": { "sourceType": "module" } in the ESLint configuration or "use strict" directive in the code:

/*eslint no-lone-blocks: "error"*/
/*eslint-env es6*/

"use strict";

{
function foo() {}
}

Version

This rule was introduced in ESLint v0.4.0.

Resources