Range of Characters and More Regular Expressions in JavaScript

The Square Brackets

A character class allows a set of possible characters, rather than just a single character, to match at a particular point in a regexp. Character classes are denoted by brackets [...], with the set of characters to be possibly matched inside. Here are some examples: 

Let your available string be

“He has a cat.”

You may know that he has an animal, but it does not matter to you which animal he has. You will be satisfied if he has a cat, bat or a rat. Note that the words, “cat”, “bat” and “rat” each have “at” but begin with a “c” or “b” or “r.” The regexp to check this is

/[bcr]at/

The following produces a match

/[bcr]at /.test(“He has a cat.”)

Here, because of the brackets, we interpret the regexp as follows: the test() function should match any word whose first character is a “b,” “c” or “r,” the rest of the characters being "at."

The square brackets denote a class of elements. However, it is any one element in the class that is to be tested, not all of them together.