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10.1.2 Character Classes

If you can’t remember exactly which punctuation characters need to be escaped with a backslash, you may safely place a backslash before any punctuation character. On the other hand, note that many letters and numbers have special meaning when preceded by a backslash, so any letters or numbers that you want to match literally should not be escaped with a backslash. To include a backslash character literally in a regular expression, you must escape it with a backslash, of course. For example, the following regular expression matches any string that includes a backslash: /\\/.


10.1.2 Character Classes

Individual literal characters can be combined into character classes by placing them within square brackets. A character class matches any one character that is contained within it. Thus, the regular expression /[abc]/ matches any one of the letters a, b, or

c. Negated character classes can also be defined; these match any character except those contained within the brackets. A negated character class is specified by placing a caret (^) as the first character inside the left bracket. The regexp /[^abc]/ matches any one character other than a, b, or c. Character classes can use a hyphen to indicate a range of characters. To match any one lowercase character from the Latin alphabet, use /[a-z]/and to match any letter or digit from the Latin alphabet, use /[a-zA-Z0-9]/.

Because certain character classes are commonly used, the JavaScript regular-expression syntax includes special characters and escape sequences to represent these common classes. For example, \s matches the space character, the tab character, and any other Unicode whitespace character; \S matches any character that is not Unicode white-space. Table 10-2 lists these characters and summarizes character-class syntax. (Note that several of these character-class escape sequences match only ASCII characters and

10.1 Defining Regular Expressions | 253

have not been extended to work with Unicode characters. You can, however, explicitly define your own Unicode character classes; for example, /[\u0400-\u04FF]/ matches any one Cyrillic character.)

Table 10-2. Regular expression character classes

Character Matches
[...] Any one character between the brackets.
[^...] Any one character not between the brackets.
. Any character except newline or another Unicode line terminator.
\w Any ASCII word character. Equivalent to [a-zA-Z0-9_].
\W Any character that is not an ASCII word character. Equivalent to [^a-zA-Z0-9_].
\s Any Unicode whitespace character.
\S Any character that is not Unicode whitespace. Note that \wand \Sare not the same thing.
\d Any ASCII digit. Equivalent to [0-9].
\D Any character other than an ASCII digit. Equivalent to [^0-9].
[\b] A literal backspace (special case).
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