A regular expression object, or any object that has a Symbol.match method.

If regexp is not a RegExp object and does not have a Symbol.match method, it is implicitly converted to a RegExp by using new RegExp(regexp).

If you don't give any parameter and use the match() method directly, you will get an Array with an empty string: [""], because this is equivalent to match(/(?:)/).

An Array whose contents depend on the presence or absence of the global (g) flag, or null if no matches are found.

• If the g flag is used, all results matching the complete regular expression will be returned, but capturing groups are not included.
• If the g flag is not used, only the first complete match and its related capturing groups are returned. In this case, match() will return the same result as RegExp.prototype.exec() (an array with some extra properties).

The implementation of String.prototype.match itself is very simple — it simply calls the Symbol.match method of the argument with the string as the first parameter. The actual implementation comes from RegExp.prototype[@@match]().

• If you need to know if a string matches a regular expression RegExp, use RegExp.prototype.test().
• If you only want the first match found, you might want to use RegExp.prototype.exec() instead.
• If you want to obtain capture groups and the global flag is set, you need to use RegExp.prototype.exec() or String.prototype.matchAll() instead.

For more information about the semantics of match() when a regex is passed, see RegExp.prototype[@@match]().