Overly complicated regular expressions are hard to read and to maintain and can easily cause hard-to-find bugs. If a regex is too complicated, you
should consider replacing it or parts of it with regular code or splitting it apart into multiple patterns at least.
The complexity of a regular expression is determined as follows:
Each of the following operators increases the complexity by an amount equal to the current nesting level and also increases the current nesting
level by one for its arguments:
-
| - when multiple | operators are used together, the subsequent ones only increase the complexity by 1
- Quantifiers (
*, +, ?, {n,m}, {n,} or {n})
- Lookahead and lookbehind assertions
Additionally, each use of the following features increase the complexity by 1 regardless of nesting:
- character classes
- back references
If a regular expression is split among multiple variables, the complexity is calculated for each variable individually, not for the whole regular
expression.
Noncompliant Code Example
const datePattern = /^(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[13-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})$/;
if (dateString.match(datePattern)) {
handleDate(dateString);
}
Compliant Solution
const datePattern = /^\d{1,2}([-/.])\d{1,2}\1\d{1,4}$/;
if (dateString.match(datePattern)) {
const dateParts = dateString.split(/[-/.]/);
const day = parseInt(dateParts[0]);
const month = parseInt(dateParts[1]);
const year = parseInt(dateParts[2]);
// Put logic to validate and process the date based on its integer parts here
}
