eslint/docs/src/rules/no-lone-blocks.md

   1 ---
   2 title: no-lone-blocks
   3 layout: doc
   4 rule_type: suggestion
   5 ---
   6
   7
   8 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`:
   9
  10 ```js
  11 {
  12     var foo = bar();
  13 }
  14 ```
  15
  16 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.
  17
  18 ## Rule Details
  19
  20 This rule aims to eliminate unnecessary and potentially confusing blocks at the top level of a script or within other blocks.
  21
  22 Examples of **incorrect** code for this rule:
  23
  24 ::: incorrect
  25
  26 ```js
  27 /*eslint no-lone-blocks: "error"*/
  28
  29 {}
  30
  31 if (foo) {
  32     bar();
  33     {
  34         baz();
  35     }
  36 }
  37
  38 function bar() {
  39     {
  40         baz();
  41     }
  42 }
  43
  44 {
  45     function foo() {}
  46 }
  47
  48 {
  49     aLabel: {
  50     }
  51 }
  52
  53 class C {
  54     static {
  55         {
  56             foo();
  57         }
  58     }
  59 }
  60 ```
  61
  62 :::
  63
  64 Examples of **correct** code for this rule with ES6 environment:
  65
  66 ::: correct
  67
  68 ```js
  69 /*eslint no-lone-blocks: "error"*/
  70 /*eslint-env es6*/
  71
  72 while (foo) {
  73     bar();
  74 }
  75
  76 if (foo) {
  77     if (bar) {
  78         baz();
  79     }
  80 }
  81
  82 function bar() {
  83     baz();
  84 }
  85
  86 {
  87     let x = 1;
  88 }
  89
  90 {
  91     const y = 1;
  92 }
  93
  94 {
  95     class Foo {}
  96 }
  97
  98 aLabel: {
  99 }
 100
 101 class C {
 102     static {
 103         lbl: {
 104             if (something) {
 105                 break lbl;
 106             }
 107
 108             foo();
 109         }
 110     }
 111 }
 112 ```
 113
 114 :::
 115
 116 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:
 117
 118 ::: correct
 119
 120 ```js
 121 /*eslint no-lone-blocks: "error"*/
 122 /*eslint-env es6*/
 123
 124 "use strict";
 125
 126 {
 127     function foo() {}
 128 }
 129 ```
 130
 131 :::