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

   1 ---
   2 title: no-nonoctal-decimal-escape
   3 layout: doc
   4 rule_type: suggestion
   5 related_rules:
   6 - no-octal-escape
   7 further_reading:
   8 - https://tc39.es/ecma262/#prod-annexB-NonOctalDecimalEscapeSequence
   9 ---
  10
  11
  12
  13
  14
  15 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:
  16
  17 ```js
  18 "\8" === "8"; // true
  19 "\9" === "9"; // true
  20 ```
  21
  22 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.
  23
  24 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.
  25
  26 Regardless of your targeted environment, these escape sequences shouldn't be used when writing new code.
  27
  28 ## Rule Details
  29
  30 This rule disallows `\8` and `\9` escape sequences in string literals.
  31
  32 Examples of **incorrect** code for this rule:
  33
  34 ::: incorrect
  35
  36 ```js
  37 /*eslint no-nonoctal-decimal-escape: "error"*/
  38
  39 "\8";
  40
  41 "\9";
  42
  43 var foo = "w\8less";
  44
  45 var bar = "December 1\9";
  46
  47 var baz = "Don't use \8 and \9 escapes.";
  48
  49 var quux = "\0\8";
  50 ```
  51
  52 :::
  53
  54 Examples of **correct** code for this rule:
  55
  56 ::: correct
  57
  58 ```js
  59 /*eslint no-nonoctal-decimal-escape: "error"*/
  60
  61 "8";
  62
  63 "9";
  64
  65 var foo = "w8less";
  66
  67 var bar = "December 19";
  68
  69 var baz = "Don't use \\8 and \\9 escapes.";
  70
  71 var quux = "\0\u0038";
  72 ```
  73
  74 :::