Quantifiers modify the previous atom and request the particular number of repetitions. An atom is a character or character class or a string literal or a group (we will talk about groups later in the Extracting substrings with capturing section of this chapter).

The + quantifier allows the previous atom to be repeated one or more times. For example, the regex /a+/ matches with a single character a, as well as with a string containing two characters aa, or three, or more—aaaaaa. It will not, however, match with a string that does not contain the a character at all.

The * quantifier allows any number of repetitions, including zero. So, the /a*/ regex matches with strings such as bdef, abc, or baad. Of course, a single /a*/ may not be that useful; the * quantifier's more natural use case is between other substrings, such as...