no-control-regex

Disallow control characters in regular expressions

Control characters are special, invisible characters in the ASCII range 0-31. These characters are rarely used in JavaScript strings so a regular expression containing elements that explicitly match these characters is most likely a mistake.

Rule Details

This rule disallows control characters and some escape sequences that match control characters in regular expressions.

The following elements of regular expression patterns are considered possible errors in typing and are therefore disallowed by this rule:

• Hexadecimal character escapes from \x00 to \x1F.
• Unicode character escapes from \u0000 to \u001F.
• Unicode code point escapes from \u{0} to \u{1F}.
• Unescaped raw characters from U+0000 to U+001F.

Control escapes such as \t and \n are allowed by this rule.

Examples of incorrect code for this rule:

/*eslint no-control-regex: "error"*/

var pattern1 = /\x00/;
var pattern2 = /\x0C/;
var pattern3 = /\x1F/;
var pattern4 = /\u000C/;
var pattern5 = /\u{C}/u;
var pattern6 = new RegExp("\x0C"); // raw U+000C character in the pattern
var pattern7 = new RegExp("\\x0C"); // \x0C pattern

Examples of correct code for this rule:

/*eslint no-control-regex: "error"*/

var pattern1 = /\x20/;
var pattern2 = /\u0020/;
var pattern3 = /\u{20}/u;
var pattern4 = /\t/;
var pattern5 = /\n/;
var pattern6 = new RegExp("\x20");
var pattern7 = new RegExp("\\t");
var pattern8 = new RegExp("\\n");

Known Limitations

When checking RegExp constructor calls, this rule examines evaluated regular expression patterns. Therefore, although this rule intends to allow syntax such as \t, it doesn’t allow new RegExp("\t") since the evaluated pattern (string value of "\t") contains a raw control character (the TAB character).

/*eslint no-control-regex: "error"*/

new RegExp("\t"); // disallowed since the pattern is: <TAB>

new RegExp("\\t"); // allowed since the pattern is: \t

There is no difference in behavior between new RegExp("\t") and new RegExp("\\t"), and the intention to match the TAB character is clear in both cases. They are equally valid for the purpose of this rule, but it only allows new RegExp("\\t").

When Not To Use It

If you need to use control character pattern matching, then you should turn this rule off.

Related Rules

• no-div-regex
• no-regex-spaces

Version

This rule was introduced in ESLint v0.1.0.

Resources

• Rule source
• Tests source