HTMLInputElement: pattern property

The pattern property of the HTMLInputElement interface represents a regular expression a non-null <input> value should match. It reflects the <input> element's pattern attribute.

The pattern property is valid for text, search, url, tel, email, and password types. It defines a regular expression that the input's value must match in order for the value to pass constraint validation.

If a non-null value doesn't conform to the constraints set by the pattern value, the ValidityState object's read-only patternMismatch property will be true.

const inputElement = document.getElementById("year");
console.log(input.pattern);