noNonoctalDecimalEscape

JavaScript (and super languages)

Summary

Rule available since: v1.0.0
Diagnostic Category: lint/correctness/noNonoctalDecimalEscape
This rule is recommended, which means is enabled by default.
This rule has a safe fix.
The default severity of this rule is error.
Sources:
- Same as no-nonoctal-decimal-escape

How to configure

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{
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  "linter": {
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    "rules": {
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      "correctness": {
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        "noNonoctalDecimalEscape": "error"
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      }
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    }
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  }
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}

Description

Disallow \8 and \9 escape sequences in string literals.

Since ECMAScript 2021, the escape sequences \8 and \9 have been defined as non-octal decimal escape sequences. However, most JavaScript engines consider them to be “useless” escapes. For example:

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"\8" === "8"; // true
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"\9" === "9"; // true

Although this syntax is deprecated, it is still supported for compatibility reasons. If the ECMAScript host is not a web browser, this syntax is optional. However, web browsers are still required to support it, but only in non-strict mode. Regardless of your targeted environment, it is recommended to avoid using these escape sequences in new code.

Examples

Invalid

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const x = "\8";

code-block.js:1:12 lint/correctness/noNonoctalDecimalEscape  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Don’t use &#92;8 and &#92;9 escape sequences in string literals.
  
  > 1 │ const x = “\8”;
      │            ^^
    2 │ 
  
  ℹ The nonoctal decimal escape is a deprecated syntax that is left for compatibility and should not be used.
  
  ℹ Safe fix: Replace \8 with 8. This maintains the current functionality.
  
    1 │ const·x·=·“\8”;
      │            -

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const x = "Don't use \8 escape.";

code-block.js:1:22 lint/correctness/noNonoctalDecimalEscape  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Don’t use &#92;8 and &#92;9 escape sequences in string literals.
  
  > 1 │ const x = “Don’t use \8 escape.”;
      │                      ^^
    2 │ 
  
  ℹ The nonoctal decimal escape is a deprecated syntax that is left for compatibility and should not be used.
  
  ℹ Safe fix: Replace \8 with 8. This maintains the current functionality.
  
    1 │ const·x·=·“Don’t·use·\8·escape.”;
      │                      -

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const x = "Don't use \9 escape.";

code-block.js:1:22 lint/correctness/noNonoctalDecimalEscape  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Don’t use &#92;8 and &#92;9 escape sequences in string literals.
  
  > 1 │ const x = “Don’t use \9 escape.”;
      │                      ^^
    2 │ 
  
  ℹ The nonoctal decimal escape is a deprecated syntax that is left for compatibility and should not be used.
  
  ℹ Safe fix: Replace \9 with 9. This maintains the current functionality.
  
    1 │ const·x·=·“Don’t·use·\9·escape.”;
      │                      -

Valid

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const x = "8";

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const x = "Don't use \\8 and \\9 escapes.";