Back reference in a regular expression should be used after the referred group

• BAD_BACK_REFERENCE_IN_REGEXP
• Error
• Medium
• No tags

This rule applies when a back reference in a regular expression is used before the referred group matches.

A back reference like \1 is used to refer the input characters previously matched by a capture group. For example, /(foo|bar)\1/ will match foofoo or barbar but not foobar.

However, when a back reference is placed before the referred group, it will always match just the empty string. This is not likely to be a programmer's intent.

Noncompliant Code Example

const re = /\1(foo|bar)/; // BAD_BACK_REFERENCE_IN_REGEXP alarm because the referred group '(foo|bar)` appears after the reference '\1'.

Compliant Code Example

const re = /(foo|bar)\1/;

Version

This rule was introduced in DeepScan 1.30.0.

See

• Backreference