Disallow Unnecessary Nested Blocks (no-lone-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.

The following patterns are considered problems:

/*eslint no-lone-blocks: 2*/

{}                    /*error Block is redundant.*/

if (foo) {
    bar();
    {                 /*error Nested block is redundant.*/
        baz();
    }
}

function bar() {
    {                 /*error Nested block is redundant.*/
        baz();
    }
}

{                     /*error Block is redundant.*/
    function foo() {}
}

The following patterns are not considered problems:

/*eslint-env es6*/
/*eslint no-lone-blocks: 2*/

while (foo) {
    bar();
}

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

function bar() {
    baz();
}

{
    let x = 1;
}

{
    const y = 1;
}

{
    class Foo {}
}

In strict mode, with ecmaFeatures: { blockBindings: true }, the following will not warn:

/*eslint-env es6*/
/*eslint no-lone-blocks: 2*/
"use strict";

{
    function foo() {}
}

Version

This rule was introduced in ESLint 0.4.0.

Resources