Range of Characters and More Regular Expressions in JavaScript

The “-“ Character

There may come a time when you want to match any occurrence of a digit between 0 to 9, or a lower case character between "a" and "z," or an uppercase character between A to Z, in an available string. These are ranges of characters, and for each range you would want to know if one character in the range exists in the available string (I will address the issue of multiple occurrences of a character of a range in the available string later).

The “-“ character is used for this. So the range 0 to 9 is denoted by 1-9; ‘a’ to ‘z’ by a-z; and A to Z by A-Z.

The following code produces a match:

/[0-9]/.test(“ID5id”)

Recall that the square brackets indicate that any element it contains should be tested. So a match occurs between 5 in the range 1 to 9 and 5 in the unavailable string “ID5id.”

The above expression is the same as

/[0123456789]/.test(“ID5id”)

The following code will produce a match for a similar reason:

/[a-z]/.test("ID5i")

A match occurs between ‘i’ in the range a-z and ‘i’, the only lowercase letter in our present available string.

Of course you can combine a range with other characters in the regular expressions. The regexps /ID[0-9]id/ will match “ID4id,” “ID5id” and “ID6id”; in fact, it will match any word beginning with "ID" followed by a digit and then "id." So

/ID[0-9]id/.test(“ID2id is an ID”)

produces a match.

Note: the range format gives a short form of writing a class. It is any one element in the square brackets that is matched.

We have done a lot so far, but there are still many things to be learned. Regular Expressions is a relatively new concept in software programming. So, we shall continue to take it step by step.

We have finished with the idea of range of characters. This is a good place to take a break. We continue in the next part of the series.