eslint/docs/src/rules/no-nonoctal-decimal-escape.md

   1 ---
   2 title: no-nonoctal-decimal-escape
   3 rule_type: suggestion
   4 related_rules:
   5 - no-octal-escape
   6 further_reading:
   7 - https://tc39.es/ecma262/#prod-annexB-NonOctalDecimalEscapeSequence
   8 ---
   9
  10
  11
  12
  13
  14 Although not being specified in the language until ECMAScript 2021, `\8` and `\9` escape sequences in string literals were allowed in most JavaScript engines, and treated as "useless" escapes:
  15
  16 ```js
  17 "\8" === "8"; // true
  18 "\9" === "9"; // true
  19 ```
  20
  21 Since ECMAScript 2021, these escape sequences are specified as [non-octal decimal escape sequences](https://tc39.es/ecma262/#prod-annexB-NonOctalDecimalEscapeSequence), retaining the same behavior.
  22
  23 Nevertheless, the ECMAScript specification treats `\8` and `\9` in string literals as a legacy feature. This syntax is optional if the ECMAScript host is not a web browser. Browsers still have to support it, but only in non-strict mode.
  24
  25 Regardless of your targeted environment, these escape sequences shouldn't be used when writing new code.
  26
  27 ## Rule Details
  28
  29 This rule disallows `\8` and `\9` escape sequences in string literals.
  30
  31 Examples of **incorrect** code for this rule:
  32
  33 ::: incorrect
  34
  35 ```js
  36 /*eslint no-nonoctal-decimal-escape: "error"*/
  37
  38 "\8";
  39
  40 "\9";
  41
  42 var foo = "w\8less";
  43
  44 var bar = "December 1\9";
  45
  46 var baz = "Don't use \8 and \9 escapes.";
  47
  48 var quux = "\0\8";
  49 ```
  50
  51 :::
  52
  53 Examples of **correct** code for this rule:
  54
  55 ::: correct
  56
  57 ```js
  58 /*eslint no-nonoctal-decimal-escape: "error"*/
  59
  60 "8";
  61
  62 "9";
  63
  64 var foo = "w8less";
  65
  66 var bar = "December 19";
  67
  68 var baz = "Don't use \\8 and \\9 escapes.";
  69
  70 var quux = "\0\u0038";
  71 ```
  72
  73 :::