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();
}
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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:

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

{}

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

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

{
    function foo() {}
}

{
    aLabel: {
    }
}

class C {
    static {
        {
            foo();
        }
    }
}
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Examples of correct code for this rule:

Open in Playground

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

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();
        }
    }
}
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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:

Open in Playground

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

"use strict";

{
    function foo() {}
}
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Version

This rule was introduced in ESLint v0.4.0.

Resources

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